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MERRION ET AL., DBA MERRION & BAYLESS, ET AL.
v.
JICARILLA APACHE TRIBE ET AL.
Supreme Court of United States.
*132 Jason W. Kellahin reargued the cause for the petitioners in No. 80-11. With him on the briefs were Bruce D. Black, Thomas H. Burton, and John Wimbish. John R. Cooney reargued the cause for petitioners in No. 80-15. With him on the briefs were Mark B. Thompson III, John H. Pickering, Samuel A. Stern, R. H. Landt, and Richard L. Marlar.
Deputy Solicitor General Claiborne reargued the cause for respondent Secretary of the Interior in both cases. With him on the brief on reargument were Acting Solicitor General Wallace and Assistant Attorney General Dinkins. With him on the brief on the original argument were Solicitor General McCree, Acting Assistant Attorney General Liotta, Edwin S. Kneedler, Jacques B. Gelin, and Martin W. Matzen. Robert J. Nordhaus reargued the cause for respondents Jicarilla Apache Tribe et al. in both cases. With him on the briefs were B. Reid Haltom and Terry D. Farmer.[โ]
Briefs of amici curiae urging affirmance were filed by Harry R. Sachse, Reid Peyton Chambers, Charles A. Hobbs, Robert A. Warden, Lawrence White, and Steven S. Anderson for the Council of Energy Resource Tribes et al.; and by George P. Vlassis for the Navajo Tribe of Indians.
*133 JUSTICE MARSHALL delivered the opinion of the Court.
Pursuant to long-term leases with the Jicarilla Apache Tribe, petitioners, 21 lessees, extract and produce oil and gas from the Tribe's reservation lands. In these two consolidated cases, petitioners challenge an ordinance enacted by the Tribe imposing a severance tax on "any oil and natural gas severed, saved and removed from Tribal lands." See Oil and Gas Severance Tax No. 77-0-02, App. 38. We granted certiorari to determine whether the Tribe has the authority to impose this tax, and, if so, whether the tax imposed by the Tribe violates the Commerce Clause.
I
The Jicarilla Apache Tribe resides on a reservation in northwestern New Mexico. Established by Executive Order in 1887,[1] the reservation contains 742,315 acres, all of which are held as tribal trust property. The 1887 Executive *134 Order set aside public lands in the Territory of New Mexico for the use and occupation of the Jicarilla Apache Indians, and contained no special restrictions except for a provision protecting pre-existing rights of bona fide settlers.[2] Approximately 2,100 individuals live on the reservation, with the majority residing in the town of Dulce, N. M., near the Colorado border.
The Tribe is organized under the Indian Reorganization Act of 1934, ch. 576, 48 Stat. 984, 25 U. S. C. ง 461 et seq., which authorizes any tribe residing on a reservation to adopt a constitution and bylaws, subject to the approval of the Secretary of the Interior (Secretary).[3] The Tribe's first Constitution, approved by the Secretary on August 4, 1937, preserved all powers conferred by ง 16 of the Indian Reorganization Act of 1934, ch. 576, 48 Stat. 987, 25 U. S. C. ง 476. In 1968, the Tribe revised its Constitution to specify:
"The inherent powers of the Jicarilla Apache Tribe, including those conferred by Section 16 of the Act of June 18, 1934 (48 Stat. 984), as amended, shall vest in the tribal council and shall be exercised thereby subject only to limitations imposed by the Constitution of the United States, applicable Federal statutes and regulations of *135 the Department of the Interior, and the restrictions established by this revised constitution." Revised Constitution of the Jicarilla Apache Tribe, Art. XI, ง 1.
The Revised Constitution provides that "[t]he tribal council may enact ordinances to govern the development of tribal lands and other resources," Art. XI, ง 1(a)(3). It further provides that "[t]he tribal council may levy and collect taxes and fees on tribal members, and may enact ordinances, subject to approval by the Secretary of the Interior, to impose taxes and fees on non-members of the tribe doing business on the reservation," Art. XI, ง 1(e). The Revised Constitution was approved by the Secretary on February 13, 1969.
To develop tribal lands, the Tribe has executed mineral leases encompassing some 69% of the reservation land. Beginning in 1953, the petitioners entered into leases with the Tribe. The Commissioner of Indian Affairs, on behalf of the Secretary, approved these leases, as required by the Act of May 11, 1938, ch. 198, 52 Stat. 347, 25 U. S. C. งง 396a-396g (1938 Act). In exchange for a cash bonus, royalties, and rents, the typical lease grants the lessee "the exclusive right and privilege to drill for, mine, extract, remove, and dispose of all the oil and natural gas deposits in or under" the leased land for as long as the minerals are produced in paying quantities. App. 22. Petitioners may use oil and gas in developing the lease without incurring the royalty. Id., at 24. In addition, the Tribe reserves the rights to use gas without charge for any of its buildings on the leased land, and to take its royalties in kind. Id., at 27-28. Petitioners' activities on the leased land have been subject to taxes imposed by the State of New Mexico on oil and gas severance and on oil and gas production equipment. Id., at 129. See Act of Mar. 3, 1927, ch. 299, ง 3, 44 Stat. 1347, 25 U. S. C. ง 398c (permitting state taxation of mineral production on Indian reservations) (1927 Act).
Pursuant to its Revised Constitution, the Tribal Council adopted an ordinance imposing a severance tax on oil and gas *136 production on tribal land. See App. 38. The ordinance was approved by the Secretary, through the Acting Director of the Bureau of Indian Affairs, on December 23, 1976. The tax applies to "any oil and natural gas severed, saved and removed from Tribal lands . . . ." Ibid. The tax is assessed at the wellhead at $0.05 per million Btu's of gas produced and $0.29 per barrel of crude oil or condensate produced on the reservation, and it is due at the time of severance. Id., at 38-39. Oil and gas consumed by the lessees to develop their leases or received by the Tribe as in-kind royalty payments are exempted from the tax. Ibid.; Brief for Respondent Jicarilla Apache Tribe 59, n. 42.
In two separate actions, petitioners sought to enjoin enforcement of the tax by either the tribal authorities or the Secretary. The United States District Court for the District of New Mexico consolidated the cases, granted other lessees leave to intervene, and permanently enjoined enforcement of the tax. The District Court ruled that the Tribe lacked the authority to impose the tax, that only state and local authorities had the power to tax oil and gas production on Indian reservations, and that the tax violated the Commerce Clause.
The United States Court of Appeals for the Tenth Circuit, sitting en banc, reversed. 617 F. 2d 537 (1980).[4] The Court of Appeals reasoned that the taxing power is an inherent attribute of tribal sovereignty that has not been divested by any treaty or Act of Congress, including the 1927 Act, 25 U. S. C. ง 398c. The court also found no Commerce Clause violation. We granted certiorari, 449 U. S. 820 (1980), and we now affirm the decision of the Court of Appeals.
II
Petitioners argue, and the dissent agrees, that an Indian tribe's authority to tax non-Indians who do business on the *137 reservation stems exclusively from its power to exclude such persons from tribal lands. Because the Tribe did not initially condition the leases upon the payment of a severance tax, petitioners assert that the Tribe is without authority to impose such a tax at a later time. We disagree with the premise that the power to tax derives only from the power to exclude. Even if that premise is accepted, however, we disagree with the conclusion that the Tribe lacks the power to impose the severance tax.
A
In Washington v. Confederated Tribes of Colville Indian Reservation, 447 U. S. 134 (1980) (Colville), we addressed the Indian tribes' authority to impose taxes on non-Indians doing business on the reservation. We held that "[t]he power to tax transactions occurring on trust lands and significantly involving a tribe or its members is a fundamental attribute of sovereignty which the tribes retain unless divested of it by federal law or necessary implication of their dependent status." Id., at 152. The power to tax is an essential attribute of Indian sovereignty because it is a necessary instrument of self-government and territorial management. This power enables a tribal government to raise revenues for its essential services. The power does not derive solely from the Indian tribe's power to exclude non-Indians from tribal lands. Instead, it derives from the tribe's general authority, as sovereign, to control economic activity within its jurisdiction, and to defray the cost of providing governmental services by requiring contributions from persons or enterprises engaged in economic activities within that jurisdiction. See, e. g., Gibbons v. Ogden, 9 Wheat. 1, 199 (1824).
The petitioners avail themselves of the "substantial privilege of carrying on business" on the reservation. Mobil Oil Corp. v. Commissioner of Taxes, 445 U. S. 425, 437 (1980); Wisconsin v. J. C. Penney Co., 311 U. S. 435, 444-445 (1940). They benefit from the provision of police protection and other governmental services, as well as from " `the advantages *138 of a civilized society' " that are assured by the existence of tribal government. Exxon Corp. v. Wisconsin Dept. of Revenue, 447 U. S. 207, 228 (1980) (quoting Japan Line, Ltd. v. County of Los Angeles, 441 U. S. 434, 445 (1979)). Numerous other governmental entities levy a general revenue tax similar to that imposed by the Jicarilla Tribe when they provide comparable services. Under these circumstances, there is nothing exceptional in requiring petitioners to contribute through taxes to the general cost of tribal government.[5] Cf. Commonwealth Edison Co. v. Montana, 453 U. S. 609, 624-629 (1981); id., at 647 (BLACKMUN, J., dissenting); Mobil Oil Corp. v. Commissioner of Taxes, supra, at 436-437.
As we observed in Colville, supra, the tribe's interest in levying taxes on nonmembers to raise "revenues for essential governmental programs . . . is strongest when the revenues are derived from value generated on the reservation by activities involving the Tribes and when the taxpayer is the recipient of tribal services." 447 U. S., at 156-157. This surely is the case here. The mere fact that the government imposing the tax also enjoys rents and royalties as the lessor of the mineral lands does not undermine the government's authority to impose the tax. See infra, at 145-148. The royalty payments from the mineral leases are paid to the Tribe in its role as partner in petitioners' commercial venture. The severance tax, in contrast, is petitioners' contribution "to the general cost of providing governmental services." Commonwealth Edison Co. v. Montana, supra, at 623. State governments commonly receive both royalty payments and severance taxes from lessees of mineral lands within their borders.
*139 Viewing the taxing power of Indian tribes as an essential instrument of self-government and territorial management has been a shared assumption of all three branches of the Federal Government. Cf. Colville, supra, at 153. In Colville, the Court relied in part on a 1934 opinion of the Solicitor for the Department of the Interior. In this opinion, the Solicitor recognized that, in the absence of congressional action to the contrary, the tribes' sovereign power to tax " `may be exercised over members of the tribe and over nonmembers, so far as such nonmembers may accept privileges of trade, residence, etc., to which taxes may be attached as conditions.' " 447 U. S., at 153 (quoting Powers of Indian Tribes, 55 I.D. 14, 46 (1934)). Colville further noted that official executive pronouncements have repeatedly recognized that "Indian tribes possess a broad measure of civil jurisdiction over the activities of non-Indians on Indian reservation lands in which the tribes have a significant interest . . . , including jurisdiction to tax." 447 U. S., at 152-153 (citing 23 Op. Atty. Gen. 214 (1900); 17 Op. Atty. Gen. 134 (1881); 7 Op. Atty. Gen. 174 (1855)).[6]
Similarly, Congress has acknowledged that the tribal power to tax is one of the tools necessary to self-government and territorial control. As early as 1879, the Senate Judiciary *140 Committee acknowledged the validity of a tax imposed by the Chickasaw Nation on non-Indians legitimately within its territory:
"We have considered [Indian tribes] as invested with the right of self-government and jurisdiction over the persons and property within the limits of the territory they occupy, except so far as that jurisdiction has been restrained and abridged by treaty or act of Congress. Subject to the supervisory control of the Federal Government, they may enact the requisite legislation to maintain peace and good order, improve their condition, establish school systems, and aid their people in their efforts to acquire the arts of civilized life; and they undoubtedly possess the inherent right to resort to taxation to raise the necessary revenue for the accomplishment of these vitally important objects โ a right not in any sense derived from the Government of the United States." S. Rep. No. 698, 45th Cong., 3d Sess., 1-2 (1879) (emphasis added).
Thus, the views of the three federal branches of government, as well as general principles of taxation, confirm that Indian tribes enjoy authority to finance their governmental services through taxation of non-Indians who benefit from those services. Indeed, the conception of Indian sovereignty that this Court has consistently reaffirmed permits no other conclusion. As we observed in United States v. Mazurie, 419 U. S. 544, 557 (1975). "Indian tribes within `Indian country' are a good deal more than `private, voluntary organizations.' " They "are unique aggregations possessing attributes of sovereignty over both their members and their territory." Ibid. See, e. g., Worcester v. Georgia, 6 Pet. 515, 557 (1832); Iron Crow v. Oglala Sioux Tribe of Pine Ridge Reservation, 231 F. 2d 89, 92, 99 (CA8 1956); Crabtree v. Madden, 54 F. 426, 428-429 (CA8 1893); Cohen, `The Spanish Origin of Indian Rights in the Law of the United States,' in The Legal Conscience 230, 234 (L. Cohen ed. *141 1960). Adhering to this understanding, we conclude that the Tribe's authority to tax non-Indians who conduct business on the reservation does not simply derive from the Tribe's power to exclude such persons, but is an inherent power necessary to tribal self-government and territorial management.
Of course, the Tribe's authority to tax nonmembers is subject to constraints not imposed on other governmental entities: the Federal Government can take away this power, and the Tribe must obtain the approval of the Secretary before any tax on nonmembers can take effect. These additional constraints minimize potential concern that Indian tribes will exercise the power to tax in an unfair or unprincipled manner, and ensure that any exercise of the tribal power to tax will be consistent with national policies.
We are not persuaded by the dissent's attempt to limit an Indian tribe's authority to tax non-Indians by asserting that its only source is the tribe's power to exclude such persons from tribal lands. Limiting the tribes' authority to tax in this manner contradicts the conception that Indian tribes are domestic, dependent nations, as well as the common understanding that the sovereign taxing power is a tool for raising revenue necessary to cover the costs of government.
Nor are we persuaded by the dissent that three early decisions upholding tribal power to tax nonmembers support this limitation. Post, at 175-183, discussing Morris v. Hitchcock, 194 U. S. 384 (1904); Buster v. Wright, 135 F. 947 (CA8 1905), appeal dism'd, 203 U. S. 599 (1906); Maxey v. Wright, 3 Ind. T. 243, 247-250, 54 S. W. 807, 809 (Ct. App. Ind. T.), aff'd, 105 F. 1003 (CA8 1900). In discussing these cases, the dissent correctly notes that a hallmark of Indian sovereignty is the power to exclude non-Indians from Indian lands, and that this power provides a basis for tribal authority to tax. None of these cases, however, establishes that the authority to tax derives solely from the power to exclude. Instead, these cases demonstrate that a tribe has the power to tax nonmembers only to the extent the nonmember enjoys the *142 privilege of trade or other activity on the reservation to which the tribe can attach a tax. This limitation on tribal taxing authority exists not because the tribe has the power to exclude nonmembers, but because the limited authority that a tribe may exercise over nonmembers does not arise until the nonmember enters the tribal jurisdiction. We do not question that there is a significant territorial component to tribal power: a tribe has no authority over a nonmember until the nonmember enters tribal lands or conducts business with the tribe. However, we do not believe that this territorial component to Indian taxing power, which is discussed in these early cases, means that the tribal authority to tax derives solely from the tribe's power to exclude nonmembers from tribal lands.
Morris v. Hitchcock, for example, suggests that the taxing power is a legitimate instrument for raising revenue, and that a tribe may exercise this power over non-Indians who receive privileges from the tribe, such as the right to trade on Indian land. In Morris, the Court approved a tax on cattle grazing and relied in part on a Report to the Senate by the Committee on the Judiciary, which found no legal defect in previous tribal tax legislation having "a twofold object โ to prevent the intrusion of unauthorized persons into the territory of the Chickasaw Nation, and to raise revenue." 194 U. S., at 389 (emphasis added). In Maxey v. Wright, the question of Indian sovereignty was not even raised: the decision turned on the construction of a treaty denying the Tribe any governing or jurisdictional authority over nonmembers. 3 Ind. T., at 247-248, 54 S. W., at 809.[7]
*143 Finally, the decision in Buster v. Wright actually undermines the theory that the tribes' taxing authority derives solely from the power to exclude non-Indians from tribal lands. Under this theory, a non-Indian who establishes lawful presence in Indian territory could avoid paying a tribal tax by claiming that no residual portion of the power to exclude supports the tax. This result was explicitly rejected in Buster v. Wright. In Buster, deeds to individual lots in Indian territory had been granted to non-Indian residents, and cities and towns had been incorporated. As a result, Congress had expressly prohibited the Tribe from removing these non-Indian residents. Even though the ownership of land and the creation of local governments by non-Indians established their legitimate presence on Indian land, the court held that the Tribe retained its power to tax. The court concluded that "[n]either the United States, nor a state, nor any other sovereignty loses the power to govern the people within its borders by the existence of towns and cities therein endowed with the usual powers of municipalities, nor by the ownership nor occupancy of the land within its territorial jurisdiction by citizens or foreigners." 135 F., at 952 (emphasis *144 added).[8] This result confirms that the Tribe's authority to tax derives not from its power to exclude, but from its power to govern and to raise revenues to pay for the costs of government.
We choose not to embrace a new restriction on the extent of the tribal authority to tax, which is based on a questionable interpretation of three early cases. Instead, based on the views of each of the federal branches, general principles of taxation, and the conception of Indian tribes as domestic, dependent nations, we conclude that the Tribe has the authority to impose a severance tax on the mining activities of petitioners as part of its power to govern and to pay for the costs of self-government.
B
Alternatively, if we accept the argument, advanced by petitioners and the dissent, that the Tribe's authority to tax derives solely from its power to exclude non-Indians from the reservation, we conclude that the Tribe has the authority to impose the severance tax challenged here. Nonmembers who lawfully enter tribal lands remain subject to the tribe's power to exclude them. This power necessarily includes the lesser power to place conditions on entry, on continued presence, or on reservation conduct, such as a tax on business activities conducted on the reservation. When a tribe grants a non-Indian the right to be on Indian land, the tribe agrees not to exercise its ultimate power to oust the non-Indian as long as the non-Indian complies with the initial conditions of entry. However, it does not follow that the lawful property right to be on Indian land also immunizes the non-Indian from the tribe's exercise of its lesser-included power to tax or to *145 place other conditions on the non-Indian's conduct or continued presence on the reservation.[9] A nonmember who enters the jurisdiction of the tribe remains subject to the risk that the tribe will later exercise its sovereign power. The fact that the tribe chooses not to exercise its power to tax when it initially grants a non-Indian entry onto the reservation does not permanently divest the tribe of its authority to impose such a tax.[10]
Petitioners argue that their leaseholds entitle them to enter the reservation and exempt them from further exercises of the Tribe's sovereign authority. Similarly, the dissent asserts that the Tribe has lost the power to tax petitioners' mining activities because it has leased to them the use of the mineral lands and such rights of access to the reservation as might be necessary to enjoy the leases. Post, at 186-190.[11] However, this conclusion is not compelled by linking the taxing power to the power to exclude. Instead, it is based on additional assumptions and confusions about the consequences of the commercial arrangement between petitioners and the Tribe.
Most important, petitioners and the dissent confuse the Tribe's role as commercial partner with its role as sovereign.[12]*146 This confusion relegates the powers of sovereignty to the bargaining process undertaken in each of the sovereign's commercial agreements. It is one thing to find that the Tribe has agreed to sell the right to use the land and take from it valuable minerals; it is quite another to find that the Tribe has abandoned its sovereign powers simply because it has not expressly reserved them through a contract.
Confusing these two results denigrates Indian sovereignty. Indeed, the dissent apparently views the tribal power to exclude, as well as the derivative authority to tax, as merely the power possessed by any individual landowner or any social group to attach conditions, including a "tax" or fee, to the entry by a stranger onto private land or into the social group, and not as a sovereign power. The dissent does pay lipservice to the established views that Indian tribes retain those fundamental attributes of sovereignty, including the power to tax transactions that occur on tribal lands, which have not been divested by Congress or by necessary implication of the tribe's dependent status, see Colville, 447 U. S., at 152, and that tribes "are a good deal more than `private, voluntary organizations.' " United States v. Mazurie, 419 U. S., at 557. However, in arguing that the Tribe somehow "lost" its power to tax petitioners by not including *147 a taxing provision in the original leases or otherwise notifying petitioners that the Tribe retained and might later exercise its sovereign right to tax them, the dissent attaches little significance to the sovereign nature of the tribal authority to tax, and it obviously views tribal authority as little more than a landowner's contractual right. This overly restrictive view of tribal sovereignty is further reflected in the dissent's refusal to apply established principles for determining whether other governmental bodies have waived a sovereign power through contract. See post, at 189, n. 50. See also infra, at 148.
Moreover, the dissent implies that the power to tax depends on the consent of the taxed as well as on the Tribe's power to exclude non-Indians. Whatever place consent may have in contractual matters and in the creation of democratic governments, it has little if any role in measuring the validity of an exercise of legitimate sovereign authority. Requiring the consent of the entrant deposits in the hands of the excludable non-Indian the source of the tribe's power, when the power instead derives from sovereignty itself. Only the Federal Government may limit a tribe's exercise of its sovereign authority. E. g., United States v. Wheeler, 435 U. S. 313, 322 (1978).[13] Indian sovereignty is not conditioned on the assent of a nonmember; to the contrary, the nonmember's presence and conduct on Indian lands are conditioned by the limitations the tribe may choose to impose.
Viewed in this light, the absence of a reference to the tax in the leases themselves hardly impairs the Tribe's authority to impose the tax. Contractual arrangements remain subject to subsequent legislation by the presiding sovereign. See, e. g., Veix v. Sixth Ward Building & Loan Assn. of *148 Newark, 310 U. S. 32 (1940); Home Building & Loan Assn. v. Blaisdell, 290 U. S. 398 (1934). Even where the contract at issue requires payment of a royalty for a license or franchise issued by the governmental entity, the government's power to tax remains unless it "has been specifically surrendered in terms which admit of no other reasonable interpretation." St. Louis v. United R. Co., 210 U. S. 266, 280 (1908).
To state that Indian sovereignty is different than that of Federal, State or local Governments, see post, at 189, n. 50, does not justify ignoring the principles announced by this Court for determining whether a sovereign has waived its taxing authority in cases involving city, state, and federal taxes imposed under similar circumstances. Each of these governments has different attributes of sovereignty, which also may derive from different sources. These differences, however, do not alter the principles for determining whether any of these governments has waived a sovereign power through contract, and we perceive no principled reason for holding that the different attributes of Indian sovereignty require different treatment in this regard. Without regard to its source, sovereign power, even when unexercised, is an enduring presence that governs all contracts subject to the sovereign's jurisdiction, and will remain intact unless surrendered in unmistakable terms.
No claim is asserted in this litigation, nor could one be, that petitioners' leases contain the clear and unmistakable surrender of taxing power required for its extinction. We could find a waiver of the Tribe's taxing power only if we inferred it from silence in the leases. To presume that a sovereign forever waives the right to exercise one of its sovereign powers unless it expressly reserves the right to exercise that power in a commercial agreement turns the concept of sovereignty on its head, and we do not adopt this analysis.[14]
*149 C
The Tribe has the inherent power to impose the severance tax on petitioners, whether this power derives from the Tribe's power of self-government or from its power to exclude. Because Congress may limit tribal sovereignty, we now review petitioners' argument that Congress, when it enacted two federal Acts governing Indians and various pieces of federal energy legislation, deprived the Tribe of its authority to impose the severance tax.
In Colville, we concluded that the "widely held understanding within the Federal Government has always been that federal law to date has not worked a divestiture of Indian taxing power." 447 U. S., at 152 (emphasis added). Moreover, we noted that "[n]o federal statute cited to us shows any congressional departure from this view." Id., at 153. Likewise, petitioners can cite to no statute that specifically divests the Tribe of its power to impose the severance tax on their mining activities. Instead, petitioners argue that Congress implicitly took away this power when it enacted the Acts and various pieces of legislation on which petitioners rely. Before reviewing this argument, we reiterate here our admonition in Santa Clara Pueblo v. Martinez, 436 U. S. 49, 60 (1978): "a proper respect both for tribal sovereignty itself and for the plenary authority of Congress in this area cautions that we tread lightly in the absence of clear indications of legislative intent."
*150 Petitioners argue that Congress pre-empted the Tribe's power to impose a severance tax when it enacted the 1938 Act, 25 U. S. C. งง 396a-396g. In essence, petitioners argue that the tax constitutes an additional burden on lessees that is inconsistent with the Act's regulatory scheme for leasing and developing oil and gas reserves on Indian land. This Act, and the regulations promulgated by the Department of the Interior for its enforcement, establish the procedures to be followed for leasing oil and gas interests on tribal lands. However, the proviso to 25 U. S. C. ง 396b states that "the foregoing provisions shall in no manner restrict the right of tribes . . . to lease lands for mining purposes . . . in accordance with the provisions of any constitution and charter adopted by any Indian tribe pursuant to sections 461, 462, 463, [464-475, 476-478], and 479 of this title" (emphasis added).[15] Therefore, this Act does not prohibit the Tribe from imposing a severance tax on petitioners' mining activities pursuant to its Revised Constitution, when both the Revised Constitution and the ordinance authorizing the tax are approved by the Secretary.[16]
Petitioners also assert that the 1927 Act, 25 U. S. C. งง 398a-398e, divested the Tribe's taxing power. We disagree. The 1927 Act permits state taxation of mineral lessees *151 on Executive Order reservations, but it indicates no change in the taxing power of the affected tribes. See 25 U. S. C. ง 398c. Without mentioning the tribal authority to tax, the Act authorizes state taxation of royalties from mineral production on all Indian lands. Petitioners argue that the Act transferred the Indian power to tax mineral production to the States in exchange for the royalties assured the tribes. This claim not only lacks any supporting evidence in the legislative history, it also deviates from settled principles of taxation: different sovereigns can enjoy powers to tax the same transactions. Thus, the mere existence of state authority to tax does not deprive the Indian tribe of its power to tax. Fort Mojave Tribe v. County of San Bernardino, 543 F. 2d 1253 (CA9 1976), cert. denied, 430 U. S. 983 (1977). Cf. Colville, 447 U. S., at 158 ("There is no direct conflict between the state and tribal schemes, since each government is free to impose its taxes without ousting the other").[17]
Finally, petitioners contend that tribal taxation of oil and gas conflicts with national energy policies, and therefore the tribal tax is pre-empted by federal law. Again, petitioners cite no specific federal statute restricting Indian sovereignty. Nor do they explain why state taxation of the same type of activity escapes the asserted conflict with federal policy. Cf. Commonwealth Edison Co. v. Montana, 453 U. S. 609 (1981). Indeed, rather than forbidding tribal severance taxes, Congress has included taxes imposed by an Indian *152 tribe in its definition of costs that may be recovered under federal energy pricing regulations. Natural Gas Policy Act of 1978, Pub. L. 95-621, งง 110(a), (c)(1), 92 Stat. 3368, 15 U. S. C. งง 3320(a), (c)(1) (1976 ed., Supp. IV). Although this inclusion may not reflect Congress' view with respect to the source of a tribe's power to impose a severance tax,[18] it surely indicates that imposing such a tax would not contravene federal energy policy and that the tribal authority to do so is not implicitly divested by that Act.
We find no "clear indications" that Congress has implicitly deprived the Tribe of its power to impose the severance tax. In any event, if there were ambiguity on this point, the doubt would benefit the Tribe, for "[a]mbiguities in federal law have been construed generously in order to comport with . . . traditional notions of sovereignty and with the federal policy of encouraging tribal independence." White Mountain Apache Tribe v. Bracker, 448 U. S. 136, 143-144 (1980). Accordingly, we find that the Federal Government has not divested the Tribe of its inherent authority to tax mining activities on its land, whether this authority derives from the Tribe's power of self-government or from its power to exclude.
III
Finding no defect in the Tribe's exercise of its taxing power, we now address petitioners' contention that the severance tax violates the "negative implications" of the Commerce Clause because it taxes an activity that is an integral *153 part of the flow of commerce, discriminates against interstate commerce, and imposes a multiple burden on interstate commerce. At the outset, we note that reviewing tribal action under the Interstate Commerce Clause is not without conceptual difficulties. E. g., nn. 21 and 24, infra. Apparently recognizing these difficulties, the Solicitor General, on behalf of the Secretary, argues that the language,[19] the structure, and the purposes of the Commerce Clause support the conclusion that the Commerce Clause does not, of its own force, limit Indian tribes in their dealings with non-Indians. Brief for Secretary of Interior 35-40. The Solicitor General reasons that the Framers did not intend "the courts, through the Commerce Clause, to impose their own views of the proper relationship between Indians and non-Indians and to strike down measures adopted by a tribe with which the political departments of government had not seen fit to disagree." Id., at 39. Instead, where tribal legislation is inimical to the national welfare, the Solicitor asserts that the Framers contemplated that the remedies would be the negotiation or renegotiation of treaties, the enactment of legislation governing trade and other relations, or the exertion of superior force by the United States Government. Id., at 38-39. Using similar reasoning, the Solicitor suggests that if the Commerce Clause does impose restrictions on tribal activity, those restrictions must arise from the Indian Commerce Clause, and not its interstate counterpart. Id., at 40-43.
To date, however, this Court has relied on the Indian Commerce Clause as a shield to protect Indian tribes from state *154 and local interference, and has not relied on the Clause to authorize tribal regulation of commerce without any constitutional restraints. We see no need to break new ground in this area today: even if we assume that tribal action is subject to the limitations of the Interstate Commerce Clause, this tax does not violate the "negative implications" of that Clause.
A
A state tax may violate the "negative implications" of the Interstate Commerce Clause by unduly burdening or discriminating against interstate commerce. See, e. g., Commonwealth Edison Co. v. Montana, 453 U. S. 609 (1981); Complete Auto Transit, Inc. v. Brady, 430 U. S. 274 (1977). Judicial review of state taxes under the Interstate Commerce Clause is intended to ensure that States do not disrupt or burden interstate commerce when Congress' power remains unexercised: it protects the free flow of commerce, and thereby safeguards Congress' latent power from encroachment by the several States.
However, we only engage in this review when Congress has not acted or purported to act. See, e. g., Prudential Insurance Co. v. Benjamin, 328 U. S. 408, 421-427 (1946). Once Congress acts, courts are not free to review state taxes or other regulations under the dormant Commerce Clause. When Congress has struck the balance it deems appropriate, the courts are no longer needed to prevent States from burdening commerce, and it matters not that the courts would invalidate the state tax or regulation under the Commerce Clause in the absence of congressional action. See Prudential Insurance Co. v. Benjamin, supra, at 431.[20] Courts are *155 final arbiters under the Commerce Clause only when Congress has not acted. See Japan Line, Ltd. v. County of Los Angeles, 441 U. S., at 454.
Here, Congress has affirmatively acted by providing a series of federal checkpoints that must be cleared before a tribal tax can take effect.[21] Under the Indian Reorganization Act, 25 U. S. C. งง 476, 477, a tribe must obtain approval from the Secretary before it adopts or revises its constitution to announce its intention to tax nonmembers. Further, before the ordinance imposing the severance tax challenged here could take effect, the Tribe was required again to obtain approval from the Secretary. See Revised Constitution of the Jicarilla Tribe, Art. XI, งง 1(e), 2. Cf. 25 U. S. C. งง 476, 477; 25 CFR ง 171.29 (1980) (implementing the proviso to 25 U. S. C. ง 396b, quoted in n. 15, supra).
As we noted earlier, the severance tax challenged by petitioners was enacted in accordance with this congressional scheme. Both the Tribe's Revised Constitution and the challenged tax ordinance received the requisite approval from the Secretary. This course of events fulfilled the administrative process established by Congress to monitor such exercises of tribal authority. As a result, this tribal tax comes to us in a *156 posture significantly different from a challenged state tax, which does not need specific federal approval to take effect, and which therefore requires, in the absence of congressional rat