What Happened?

Congress can pass laws that reach back in time, but the Constitution sets firm limits on how far, according to a Congressional Research Service report updated this month. The Congressional Research Service (CRS) is the nonpartisan agency that provides legal and policy analysis directly to Congress. The report identifies four constitutional guardrails that courts use to judge whether a retroactive law goes too far: the Ex Post Facto Clause, the Bill of Attainder Clause, the Due Process Clause, and the Takings Clause.

Why Does It Matter to Me?

A business could be forced to pay into a pension fund for workers it stopped employing decades ago. A person convicted of a crime could face new consequences, like mandatory registration on a public list, for something they did years earlier. A property owner could see rights stripped away after the fact. The CRS report makes clear that criminal and civil cases are treated differently. Criminal retroactive laws face strict limits. Civil retroactive laws face a lower bar, but courts will still strike them down if the burden on a person or company is severe and disproportionate.

Both Sides, Now

The CRS report does not frame this as a partisan debate. It describes how courts have drawn the line between what Congress may and may not do. On the side of congressional power, the Supreme Court has upheld some backward-looking criminal measures, such as laws that reduce how often a prisoner can apply for parole or require sex offender registration for past crimes. Courts have also allowed retroactive civil laws when they serve a rational purpose.

On the side of limits, courts have struck down laws that cross clear lines. In *Foretich v. United States*, a court struck down a law that altered one specific father's visitation rights, finding it punished him without a trial. In *Eastern Enterprises v. Apfel*, the Supreme Court struck down a 1992 law requiring a company that had left the coal mining industry in 1965 to pay millions into a miners' pension fund, calling the burden severe and disproportionate. The Bill of Attainder Clause is particularly relevant when Congress targets a named individual or company. A recent case, *Kaspersky Lab v. Department of Homeland Security*, shows how that line is drawn: a court upheld a ban on federal use of Kaspersky cybersecurity products because the law served national security goals rather than punishing the company directly.

What Happens Next?

The constitutional limits described in the CRS report are not new legislation. Rather, they are existing legal standards that courts apply whenever Congress passes a law with retroactive effect. Any new retroactive law passed by Congress could face a legal challenge under one or more of these clauses. Federal courts, and ultimately the Supreme Court, have the power to strike down laws that cross those lines. There is no scheduled vote or pending legislation tied to this report.

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