Article III, Section 2, Clause 2:
In all Cases affecting Ambassadors, other public Ministers and Consuls, and those in which a State shall be a Party, the supreme Court shall have original Jurisdiction. In all the other Cases before mentioned, the Supreme Court shall have appellate Jurisdiction, both as to Law and Fact, with such Exceptions, and under such Regulations as the Congress shall make.
Although the states' rights proponents in the Convention and in the First Congress wished to leave to the state courts the enforcement of federal law and rights rather than to create inferior federal courts, 1 it was not long before they or their successors began to argue that state courts could not be required to adjudicate cases based on federal law. The practice in the early years was to make the jurisdiction of federal courts generally concurrent with that of state courts, 2 and early Congresses imposed positive duties on state courts to enforce federal laws. 3 Reaction set in out of hostility to the Embargo Acts, the Fugitive Slave Law, and other measures, 4 and, in Prigg v. Pennsylvania, 5 involving the Fugitive Slave Law, the Court indicated that the states could not be compelled to enforce federal law. After a long period, however, Congress resumed its former practice, 6 which the Court sustained, 7 and it went even further in the Federal Employers' Liability Act by not only giving state courts concurrent jurisdiction but also by prohibiting the removal of cases begun in state courts to the federal courts. 8
When Connecticut courts refused to enforce an FELA claim on the ground that to do so was contrary to the public policy of the state, the Court held on the basis of the Supremacy Clause that, when Congress enacts a law and declares a national policy, that policy is as much Connecticut's and every other state's as it is of the collective United States. 9 The Court's suggestion that the act could be enforced "as of right, in the courts of the States when their jurisdiction, as prescribed by local laws, is adequate to the occasion," 10 leaving the impression that state practice might in some instances preclude enforcement in state courts, was given body when the Court upheld New York's refusal to adjudicate an FELA claim that fell in a class of cases in which claims under state law would not be entertained. 11 "[T]here is nothing in the Act of Congress that purports to force a duty upon such Courts as against an otherwise valid excuse." 12 However, "[a]n excuse that is inconsistent with or violates federal law is not a valid excuse: The Supremacy Clause forbids state courts to dissociate themselves from federal law because of disagreement with its content or a refusal to recognize the superior authority of its source." 13
The fact that a state statute divests its courts of jurisdiction not only over a disfavored federal claim, but also over an identical state claim, does not ensure that the "state law will be deemed a neutral rule of judicial administration and therefore a valid excuse for refusing to entertain a federal cause of action." 14 "Although the absence of discrimination [in its treatment of federal and state law] is necessary to our finding a state law neutral, it is not sufficient. A jurisdictional rule cannot be used as a device to undermine federal law, no matter how evenhanded it may appear." 15
In Testa v. Katt, 16 the Court unanimously held that state courts, at least with regard to claims and cases analogous to claims and cases enforceable in those courts under state law, are required to enforce "penal" laws of the United States; the statute at issue in the case provided "that a buyer of goods at above the prescribed ceiling price may sue the seller 'in any court of competent jurisdiction.'" 17 Respecting Rhode Island's claim that one sovereign cannot enforce the penal laws of another, Justice Black observed that the assumption underlying this claim flew "in the face of the fact that the States of the Union constitute a nation" and the fact of the existence of the Supremacy Clause. 18