In the case of William Fiore v. Gregory White, Warden et al., 2000, the U.S Supreme Court was asked to determine whether a state court's interpretation of its own law could be considered an "unexpected and indefensible" change that violated due process rights under federal law. The petitioner, William Fiore, had been convicted in Pennsylvania for operating a hazardous waste facility without a permit but his conviction was based on an incorrect interpretation of state law. After his conviction became final, the Pennsylvania Supreme Court clarified that operating without a permit wasn't illegal if one hadn’t been issued by authorities yet. Despite this clarification which effectively nullified Fiore’s crime retrospectively, he remained imprisoned because lower courts refused to apply it retroactively to cases like his already decided. The U.S Supreme Court unanimously held that when a State Supreme Court concludes that its prior criminal statute did not criminalize certain conduct then those whose convictions have become final must benefit from such new interpretations or clarifications as well.

In the dissenting opinion for William Fiore v. Gregory White, Warden et al., Justice Scalia argued that Pennsylvania's Supreme Court did not announce a new rule of law but rather clarified an existing one. He contended that it was incorrect to say that Fiore’s conviction became invalid when the state court later reinterpreted the statute under which he had been convicted. According to him, federal courts should defer to state courts' interpretation of their own laws unless they are clearly erroneous or violate federal law or Constitution. Therefore, he disagreed with majority's decision and believed Mr. Fiore’s habeas corpus petition should have been denied because his conviction was valid at the time it occurred based on then-existing understanding of Pennsylvania law.