Article 1, Section 9, Clause 3: Bills of Attainder; Ex Post Facto Laws
No Bill of Attainder or ex post facto Law shall be passed.
A bill of attainder is an act by a legislature that declares a person or a clearly identifiable group of persons to be guilty of a crime, and imposes punishment, without a trial. It nullifies the usual procedural protections afforded the accused within the judicial system. Bills of attainder were still being used by Parliament at the time of the American Revolution, and were one of the grievances of the colonists. The first subclause of Clause 3 prohibits Congress from enacting any bills of attainder.
This clause was uncontroversial at the time of its passage. There have, however, been notable cases defining the precise scope and meaning of the prohibition. It has been consistently interpreted to prohibit any criminal penalties imposed by a legislature on specific persons or easily identifiable groups of persons, but it remains less settled whether it applies to civil penalties or what constitutes an easily identifiable group of persons.
For example, in Ex parte Garland, the court struck down a law prohibiting attorneys from practicing in federal court unless they took an oath that they had not participated in the Confederate rebellion of the Civil War. Likewise, a 1946 law naming three federal employees whose salaries were to be reduced to $1 a year, in order to drive them out of their posts, was struck down as an ex post facto law.
During the Cold War, a number of laws that prohibited Communists from holding government or labor union positions were challenged on the grounds that these constituted bills of attainder. For the most part, such laws were upheld, but not in every case. Nowadays the courts would be much less likely to uphold such laws, requiring instead that the laws target the specific behavior held to constitute a credible public danger. Those of us who hold security clearances may have noticed that we are no longer asked if we are members of the Communist Party; we are asked instead if we are affiliated with any organization advocating the overthrow of the U.S. government by unconstitutional means. The latter almost certainly would survive a court challenge.
An ex post facto law is one that retroactively penalizes actions that have already taken place. It violates the basic principle of Ango-American law that the law must, at least in principle, be knowable so that a person can conform his behavior to the law. The prohibition on ex post facto law is largely uncontroversial except in its breadth of applicability. It is interpreted broadly, so that a change in the penalty for an act cannot be applied retroactively, nor can new rules of evidence be applied retroactively.
Laws requiring sexual offenders to register with the local police have been deemed constitutional even when applied retroactively, to convicted sex offenders whose crimes occurred before the legislation establishing the sex offender registry was enacted. The courts have reasoned that the requirements to register do not constitute criminal punishment and so are not prohibited. Likewise, laws requiring persons guilty of domestic violence, or who are under a restraining order for alleged acts of domestic violence, to surrender their firearms, have been upheld.