Interstate compacts require the consent of

Article I, Section 10, Clause 3:

No State shall, without the Consent of Congress, lay any Duty of Tonnage, keep Troops, or Ships of War in time of Peace, enter into any Agreement or Compact with another State, or with a foreign Power, or engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay.

The Compact Clause prohibits states from entering into “any Agreement or Compact with another State” or with a foreign government without the consent of Congress.1 Footnote
U.S. Const. art. I, § 10, cls. 1–2 . Whereas other provisions in Article I, Section 10 categorically deny states certain powers,2 Footnote
See U.S. Const. art. I, § 10, cls. 1–2 (prohibiting states from, among other things, entering into treaties, coining money, impairing contracts, granting titles of nobility, and regulating most imports and exports). See also ArtI.S10.C1.1.1 Foreign Policy by States to ArtI.S10.C3.3.6 Legal Effect and Interpretation of Compacts. the Compact Clause allows states to retain what the Supreme Court has described as the sovereign right to make agreements and compacts, provided Congress consents.3 Footnote
See, e.g., Poole v. Fleeger’s Lessee, 36 U.S. 185, 208–09 (1837) (explaining that the Constitution requres consent for a compact between states and that, in this instance, such consent had “been expressly given” ).

According to the Supreme Court, there is little difference between “agreements” and “compacts” in this clause.4 Footnote
See, e.g., Virginia v. Tennessee, 148 U.S. 503, 520, 537 (1893) ; Rhode Island v. Massachusetts, 37 U.S. 657, 725 (1838) . Both terms refer to contacts between governments—although a compact may reflect a more “formal and serious engagement” than an agreement.5 Footnote
Virginia , 148 U.S. at 520 . See Texas v. New Mexico, 482 U.S. 124, 128 (1987) (noting that a “Compact is, after all, a contract” between sovereigns) (quoting Petty v. Tennessee-Missouri Bridge Comm’n, 359 U.S. 275, 285 (1959) (Frankfurter, J., dissenting)); Virginia v. West Virginia, 78 U.S. 39, 59 (1870) ( “[A]greement means the mutual consent of the parties to a given proposition . . . .” ); see also Compact, Black’s Law Dictionary (11th ed. 2019) (defining “compact” as “[a]n agreement or covenant between two or more parties, esp. between governments or states” ). Because the distinctions between “Agreement” and “Compact,” are minor, this essay uses the terms interchangeably. Once approved by Congress, agreements and compacts have the force of federal law.6 Footnote
See infra ArtI.S10.C3.3.6 Legal Effect and Interpretation of Compacts. As a result, agreement and compacts have dual functions: they operate as contracts between governments and, if approved by Congress, part of the law of the United States.7 Footnote
For background on the Supremacy Clause, see infra ArtVI.C2.1 Overview of the Supremacy Clause.

The ability to form compacts with other governments is a defining characteristic of sovereignty.8 Footnote
See, e.g., Poole , 36 U.S. at 209 ; Rhode Island v. Massachusetts, 37 U.S. 657, 725 (1838) ; ArtII.S2.C2.1.2 Historical Background on the Treaty-Making Power (discussing the importance of international agreement-making to the concept of sovereignty). In the Compact Clause, the Constitution adapts the sovereign’s traditional compact-making power to the American constitutional system in which both the federal government and the states have sovereign authority.9 Footnote
See Hinderlider v. La Plata River & Cherry Creek Ditch Co., 304 U.S. 92, 104 (1938) . For discussion of the dual sovereignty doctrine, see infra Amdt5.2.3 Dual Sovereignty Doctrine. The clause safeguards national interests by giving Congress control over matters that reach beyond state lines but are not suitable for direct federal regulation.10 Footnote
See Petty v. Tennessee-Missouri Bridge Comm’n, 359 U.S. 275, 282 n.7 (1959) . See also Texas v. New Mexico , No. 141, Orig., slip op. at 4 (U.S. Mar. 5, 2018) (noting that the Compact Clause “ensures that the Legislature can ‘check any infringement of the rights of the national government.’” ) (quoting 3 Joseph Story , Commentaries on the Constitution of the United States § 1397 (1833) ); Cuyler v. Adams, 449 U.S. 433, 440 (1981) ( “[T]he Framers sought to ensure that Congress would maintain ultimate supervisory power over cooperative state action that might otherwise interfere with the full and free exercise of federal authority.” ); West Virginia ex rel. Dyer v. Sims, 341 U.S. 22, 27–28 (1951) (describing compacts as a “supple device” for addressing regional problems while protecting national interests). It also protects states’ interests by limiting an individual state’s power to form compacts that might disadvantage other states or regional interests.11 Footnote
See Florida v. Georgia, 58 U.S. 478, 494 (1854) .

A literal reading of the Compact Clause would require congressional approval for any agreement or compact.12 Footnote
See U.S. Steel Corp. v. Multistate Tax Comm’n, 434 U.S. 452, 459 (1978) . In the context of interstate compacts, however, the Supreme Court has adopted a functional interpretation in which only compacts that increase the political power of the states while undermining federal sovereignty require congressional consent.13 Footnote
See, e.g., Cuyler v. Adams, 449 U.S. 433, 440 (1981) ; U.S. Steel Corp. , 434 U.S. at 468 ; New Hampshire v. Maine, 426 U.S. 363, 369–370 (1976) ; Virginia v. Tennessee, 148 U.S. 503, 519 (1893) . For background on functionalism as a method of constitutional interpretation, see supra Intro.7.8 Structuralism and Constitutional Interpretation. The Supreme Court has not said whether the same interpretation applies to states’ compacts with foreign governments, but the proliferation of states’ pacts14 Footnote
This set of essays uses “pact” as a generic term for any international commitment to which a state is a party, regardless of its form, title, and whether it is legally binding. with foreign officials suggests Congress’s approval is not required in many cases.15 Footnote
See infra ArtI.S10.C3.3.5 Requirement of Congressional Consent to Compacts. For discussion of the effect of historical practice on constitutional interpretation, see supra Intro.7.9 Historical Practices and Constitutional Interpretation.

Footnotes 1 U.S. Const. art. I, § 10, cls. 1–2 . 2 See U.S. Const. art. I, § 10, cls. 1–2 (prohibiting states from, among other things, entering into treaties, coining money, impairing contracts, granting titles of nobility, and regulating most imports and exports). See also ArtI.S10.C1.1.1 Foreign Policy by States to ArtI.S10.C3.3.6 Legal Effect and Interpretation of Compacts. 3 See, e.g., Poole v. Fleeger’s Lessee, 36 U.S. 185, 208–09 (1837) (explaining that the Constitution requres consent for a compact between states and that, in this instance, such consent had “been expressly given” ). 4 See, e.g., Virginia v. Tennessee, 148 U.S. 503, 520, 537 (1893) ; Rhode Island v. Massachusetts, 37 U.S. 657, 725 (1838) . 5 Virginia , 148 U.S. at 520 . See Texas v. New Mexico, 482 U.S. 124, 128 (1987) (noting that a “Compact is, after all, a contract” between sovereigns) (quoting Petty v. Tennessee-Missouri Bridge Comm’n, 359 U.S. 275, 285 (1959) (Frankfurter, J., dissenting)); Virginia v. West Virginia, 78 U.S. 39, 59 (1870) ( “[A]greement means the mutual consent of the parties to a given proposition . . . .” ); see also Compact, Black’s Law Dictionary (11th ed. 2019) (defining “compact” as “[a]n agreement or covenant between two or more parties, esp. between governments or states” ). Because the distinctions between “Agreement” and “Compact,” are minor, this essay uses the terms interchangeably. 6 See infra ArtI.S10.C3.3.6 Legal Effect and Interpretation of Compacts. 7 For background on the Supremacy Clause, see infra ArtVI.C2.1 Overview of the Supremacy Clause. 8 See, e.g., Poole , 36 U.S. at 209 ; Rhode Island v. Massachusetts, 37 U.S. 657, 725 (1838) ; ArtII.S2.C2.1.2 Historical Background on the Treaty-Making Power (discussing the importance of international agreement-making to the concept of sovereignty). 9 See Hinderlider v. La Plata River & Cherry Creek Ditch Co., 304 U.S. 92, 104 (1938) . For discussion of the dual sovereignty doctrine, see infra Amdt5.2.3 Dual Sovereignty Doctrine. 10 See Petty v. Tennessee-Missouri Bridge Comm’n, 359 U.S. 275, 282 n.7 (1959) . See also Texas v. New Mexico , No. 141, Orig., slip op. at 4 (U.S. Mar. 5, 2018) (noting that the Compact Clause “ensures that the Legislature can ‘check any infringement of the rights of the national government.’” ) (quoting 3 Joseph Story , Commentaries on the Constitution of the United States § 1397 (1833) ); Cuyler v. Adams, 449 U.S. 433, 440 (1981) ( “[T]he Framers sought to ensure that Congress would maintain ultimate supervisory power over cooperative state action that might otherwise interfere with the full and free exercise of federal authority.” ); West Virginia ex rel. Dyer v. Sims, 341 U.S. 22, 27–28 (1951) (describing compacts as a “supple device” for addressing regional problems while protecting national interests). 11 See Florida v. Georgia, 58 U.S. 478, 494 (1854) . 12 See U.S. Steel Corp. v. Multistate Tax Comm’n, 434 U.S. 452, 459 (1978) . 13 See, e.g., Cuyler v. Adams, 449 U.S. 433, 440 (1981) ; U.S. Steel Corp. , 434 U.S. at 468 ; New Hampshire v. Maine, 426 U.S. 363, 369–370 (1976) ; Virginia v. Tennessee, 148 U.S. 503, 519 (1893) . For background on functionalism as a method of constitutional interpretation, see supra Intro.7.8 Structuralism and Constitutional Interpretation. 14 This set of essays uses “pact” as a generic term for any international commitment to which a state is a party, regardless of its form, title, and whether it is legally binding. 15 See infra ArtI.S10.C3.3.5 Requirement of Congressional Consent to Compacts. For discussion of the effect of historical practice on constitutional interpretation, see supra Intro.7.9 Historical Practices and Constitutional Interpretation.