In Testa et al. v. Katt, the U.S Supreme Court ruled that state courts are obligated to enforce federal laws when applicable and cannot refuse jurisdiction simply because the law in question is a federal one. The case arose after Rhode Island's court refused to hear a suit brought under the Emergency Price Control Act of 1942, arguing it was not obliged to enforce this particular piece of federal legislation due to its penal nature. However, the Supreme Court disagreed with this reasoning and held that if a state court would be competent enough to try similar cases arising under state law, then it must also accept cases based on analogous federal laws as well.

In the dissenting opinion for Testa et al. v. Katt, Justice Frankfurter argued that the Supreme Court overstepped its boundaries by forcing state courts to enforce federal laws in a manner inconsistent with their own interpretation of those laws. He contended that while states should not be allowed to ignore federal law entirely, they should have some discretion in how they apply it within their jurisdiction. This is because each state has unique circumstances and legal traditions which may require different approaches to enforcement. Furthermore, he believed this ruling undermined principles of federalism by diminishing the role and autonomy of state courts within our system of government.