CUMMINGS v. MISSOURI
Following the Civil War, Congress and Missouri adopted provisions that required persons in specified professional occupations to take an oath that they have never given aid to the rebellion and secession. Missouri convicted a priest who refused to take the oath. A former Confederate congressman asked the Supreme Court for permission to practice without taking the federal oath.
Do the state and national oaths violate prohibitions against ex post facto laws and bills of attainder of the Constitution?
Field, writing for a divided Court, held that both state and national oath laws were unconstitutional. The oath laws transformed acts that had not been forbidden into crimes and increased the punishment of acts that were known to be crimes. The oath laws were also bills of attainder since they were legislative acts that inflicted punishment without the benefit of a trial by a judge.