THE CONSTITUTION OF THE UNITED STATES OF AMERICA
Article I, Section 10
No State shall enter into any Treaty, Alliance, or Confederation; grant Letters of Marque and Reprisal; coin Money; emit Bills of Credit; make any Thing but gold and silver Coin a Tender in Payment of Debts; pass any Bill of Attainder, ex post facto Law, or Law impairing the Obligation of Contracts, or grant any Title of Nobility.
No State shall, without the Consent of the Congress, lay any Imposts or Duties on Imports or Exports, except what may be absolutely necessary for executing its inspection Laws: and the net Produce of all Duties and Imposts, laid by any State on Imports or Exports, shall be for the Use of the Treasury of the United States; and all such Laws shall be subject to the Revision and Control of the Congress.
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.