Why It Matters
The Constitution imposes four distinct legal barriers on retroactive legislation: the Ex Post Facto Clause, the Bill of Attainder Clause, the Due Process Clause, and the Takings Clause, according to a Congressional Research Service (CRS) report on retroactive legislation updated September 2.
While retroactive punishment faces strict constitutional limits, the Supreme Court has upheld some retroactive criminal measures, such as statutes that decrease the frequency of parole eligibility hearings or impose new collateral consequences like mandatory sex offender registration. A civil retroactive law may be struck down if it improperly places a severe, disproportionate, and extremely retroactive burden on a party.
The Big Picture
The Ex Post Facto Clause prohibits laws that criminalize conduct that was legal when it occurred, increase the severity of a crime after the fact, increase punishment after the crime was committed, or change evidentiary rules to make conviction easier. Courts have applied this restriction only to penal laws, not to all retroactive legislation.
In Calder v. Bull (1798), Justice Samuel Chase outlined the core prohibitions, and the Supreme Court has since upheld some retroactive criminal measures, suggesting the clause permits some backward-looking changes if they do not strictly punish past conduct.
The Bill of Attainder Clause bars statutes that directly impose punishment by legislation rather than through court proceedings. A law constitutes a bill of attainder if it applies with specificity to an identified individual or group and imposes punishment without a trial. Courts use a three-part test from Nixon v. Administrator of General Services to determine whether a law crosses this line, examining historical precedent, whether the law functions as punishment in fact, and congressional motivations.
In Kaspersky Lab v. Department of Homeland Security, a court upheld a statute barring federal use of Kaspersky cybersecurity products because it served national security goals rather than punitive ones. Conversely, in Foretich v. United States, a panel struck down a statute altering a specific father's visitation rights, finding the burden imposed outweighed implausible nonpunitive purposes.
Congress has much broader authority to enact retroactive civil laws than retroactive criminal laws. A retroactive civil law violates due process only if it is particularly harsh and oppressive or arbitrary and irrational. Yet the Supreme Court has not established firm time limits on how far back a retroactive law may reach.
The permissible period may be fact-specific. A retroactive law that deprives a person of a vested property right may also violate the Takings Clause. In Eastern Enterprises v. Apfel, the Supreme Court struck down a 1992 law requiring a company that had exited coal mining in 1965 to pay millions into a miners' pension fund, finding the statute improperly placed a severe, disproportionate, and extremely retroactive burden on the company.
The Bottom Line
Congress can create or amend a law that retroactively applies to lawsuits that began before the new law was enacted, but doing so carries constitutional risk under the Bill of Attainder Clause if the law targets a specific party and under due process if the retroactive burden is disproportionate.
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