In Warden, Lewisburg Penitentiary v. Marrero (1973), the U.S. Supreme Court ruled that a federal prisoner could not use a change in sentencing laws to challenge his continued imprisonment under an older, harsher law. The case involved Angel Marrero who was convicted of selling heroin and sentenced under the Narcotic Control Act of 1956 which required mandatory minimum sentences without parole for drug offenses. After his conviction, Congress repealed this act and replaced it with more lenient sentencing guidelines that allowed parole consideration after serving one-third or ten years of their sentence - whichever is less. Marrero filed a habeas corpus petition arguing he should be eligible for these new rules but both lower courts denied him relief on grounds that repealing statutes do not apply retroactively unless expressly declared by Congress. The Supreme Court affirmed these decisions stating that while there's presumption against applying laws retroactively, it doesn't mean every time legislature enacts new penal statute favorable to defendants then those already sentenced can benefit from them; rather such changes are prospective unless otherwise specified by lawmakers themselves.

In the dissenting opinion for Warden, Lewisburg Penitentiary v. Marrero (1973), Justice Rehnquist disagreed with the majority's interpretation of Section 4208(a)(2) and its application to federal parole eligibility rules. He argued that Congress intended this section to provide flexibility in sentencing by allowing judges to make an inmate eligible for parole at any time, regardless of mandatory minimum sentences set out elsewhere in law. According to him, it was not meant as a tool for courts or prisoners themselves to bypass these mandatory minimums entirely after they had been imposed. Furthermore, he contended that if Congress wanted such a significant change in policy - effectively reducing many inmates' sentences - it would have done so explicitly rather than through ambiguous language buried within a larger statute.