In the Bouie v. City of Columbia case in 1963, two African American petitioners were convicted for trespassing after refusing to leave a segregated restaurant in South Carolina. The Supreme Court ruled that their convictions violated the Due Process Clause of the Fourteenth Amendment because they had no fair warning at the time of their conduct that it was criminal since segregation laws did not explicitly state that remaining on premises after being asked to leave constituted trespassing. The court held that applying a new interpretation retroactively made an unforeseeable judicial enlargement of a criminal statute and thus, infringed upon due process rights by failing to give notice as required under Ex Post Facto principles. Therefore, this landmark decision expanded constitutional protections against ex post facto laws beyond legislative acts to include judicial rulings.

In the dissenting opinion for Bouie et al. v. City of Columbia, Justice Harlan argued that the majority's decision was a departure from established principles of due process and ex post facto laws. He contended that there was no violation of due process because the petitioners were not charged with an offense they could not have known to be criminal at the time it was committed; rather, they deliberately chose to violate a law whose application had been clarified by state courts after their arrest but before their trial. Furthermore, he disagreed with applying an ex post facto analysis to this case as traditionally such concerns apply only in cases where legislative action changes punishment or definition of crimes retrospectively. The interpretation made by South Carolina Supreme Court did not create new obligations or impose new duties but merely gave precision to what already existed under its trespass law.