In the 1986 case Miller v. Florida, the U.S. Supreme Court ruled that a state cannot retroactively increase punishment for criminal acts after they have been committed. The defendant, James Miller, was convicted of sexual battery in Florida and sentenced under guidelines effective at his time of sentencing but not when he committed his crime. These new guidelines resulted in a longer sentence than what would have been imposed under the old ones. The court held this to be an ex post facto law - one that changes legal consequences of actions after they were performed - which is prohibited by Article I Section 10 of the Constitution. Therefore, it violated Miller's rights as it increased his punishment retrospectively.

In the dissenting opinion for Miller v. Florida, Justice Powell argued that the majority's decision was inconsistent with previous rulings and undermined the principle of finality in sentencing. He believed that a defendant should not be able to challenge their sentence after it has been finalized simply because new guidelines have since been established which would result in a lesser punishment if applied retroactively. In his view, this could potentially open up countless sentences to reevaluation every time sentencing guidelines are revised or updated, creating an untenable situation for courts and undermining public confidence in the justice system. Furthermore, he contended that there was no violation of ex post facto laws as they were intended to prevent legislative bodies from increasing punishments retrospectively rather than preventing judicial bodies from applying new rules prospectively.