The Supreme Court overturned statutes requiring loyalty oaths, viewing them as unconstitutional ex post facto laws and bills of attainder.
Justice Stephen J. Field
One of Justice Stephen J. Field's principal objections to loyalty oath statutes was that they constituted a form of ex post facto law.
Field noted that, although these statutes did not impose fines or imprisonment, they were punitive because they banned those who could not take oaths honestly from practicing their professions. Sections 9 and 10 of Article I of the U.S. Constitution ban bills of attainder and ex post facto laws at the state and federal level. Field found the statutes in Cummings and Garland to be ex post facto retroactive legislation (laws that criminalized acts considered legal when committed) and bills of attainder because they imposed punishment without trial to a designated group of individuals. Miller, in dissent, argued that the statutes were not imposing punishment and therefore could not be either bills of attainder or ex post facto laws. This decision, never repudiated by the Supreme Court, was used in United States v. Brown
Bill of attainder
Dennis v. United States
Ex post facto laws
Scales v. United States
Yates v. United States