Harry Keyishian began teaching at the private University of Buffalo in 1960 as an instructor in English. In 1962, the University of Buffalo joined the State University of New York. As a state institution, it began requiring its employees to sign a loyalty oath as prescribed by the Feinberg Law. The Feinberg Law, enacted in 1949, was largely seen as an anti-Communism law that sought to prevent subversive persons from holding teaching positions in New York State.

Keyishian refused to sign the Feinberg Loyalty oath and consequently, in 1964, his instructorship was not renewed. Keyishian's decision may have been influenced by his experiences as a student at Queens College where, in the 1950s, two professors' positions were terminated when they refused to answer questions about their involvement with the Communist Party in America.

After his position was not renewed, Keyishian joined with four other University at Buffalo employees who refused to take the loyalty oath: Newton Garver, George Starbuck, Ralph Maud and George Hochfield. Together, they were represented by Richard Lipsitz who argued that precedents upholding Feinberg and similar state laws should not apply to post-secondary school teachers.

Though a federal district court ruled against them, their case was appealed to the United States Supreme Court. In January 1967, the Supreme Court handed down a 5-4 decision in their favor, thus overturning the Feinberg Law in New York State.

In 1965, after completing the requirements for his Ph.D., Harry Keyishian was hired as a professor at Fairleigh Dickenson University in New Jersey. He taught English there until his retirement in 2007.

Source: "Reflections by an academic freedom pioneer." by David L. Hudson Jr. firstamendmentcenter.org: analysis. Sept. 26, 2007.