In the 1950s, the "Red Scare" that accompanied McCarthyism resulted in laws that forced public officials to confirm their loyalty to the U.S. and deny any affiliation with the Communist party. One law enacted in New York State allowed schools to fire teachers who belonged to "subversive organizations." The state teacher's union told the teachers to refuse to answer, since the question itself violated another state law. Those teachers were all fired.
The union then sued the state board of education. Math teacher Irving Adler's name is associated with the case because it appeared first on court documents. The case eventually went to the Supreme Court, which ruled in 1952 that a law firing teachers who were members of subversive organizations was neither vague nor in violation of freedom of speech or due process.
In the early 1960s, with the same archaic laws on the books in New York State, professor Harry Keyishian found himself employed by a private university in the process of merging with a state university. He refused to take the loyalty oath and was dismissed. In the case of Keyishian v. Board of Regents of the University of the State of New York, the Supreme Court ruled that the state law was too vague to be constitutional (you can't receive your guaranteed due process under the law if you can't understand it), and that it was also an unconstitutional suppression of free speech and academic freedom.
The teachers who had been fired in the 50s sued for their jobs, and won.