In the case of Marks et al. v. United States, the Supreme Court was tasked with determining whether a change in law could be applied retroactively to past convictions. The appellants were convicted for transporting obscene materials across state lines under federal obscenity laws that had been redefined by a previous Supreme Court ruling (Miller v. California). They argued that their actions were not illegal under the new definition at the time they committed them and thus their convictions should be overturned. The court ruled 5-3 against this argument, stating that even though there may have been changes in how obscenity was defined legally, it did not mean those who violated prior definitions would automatically have their sentences invalidated or reduced as a result of these changes. This decision established an important precedent regarding retroactive application of law changes: unless explicitly stated otherwise by Congress or if it is necessary to prevent gross injustice, new rulings do not apply retrospectively.

In the dissenting opinion for Marks v. United States, Justice William Rehnquist argued that the majority's decision to apply a new standard retroactively was inappropriate and inconsistent with previous court decisions. He contended that this ruling would unfairly penalize defendants who had acted in accordance with existing laws at the time of their actions. Furthermore, he expressed concern about potential confusion and uncertainty caused by changing legal standards after-the-fact. In his view, such changes should only be applied prospectively to ensure fairness and predictability in law enforcement and judicial proceedings.