In the case of Clay, also known as Ali v. United States in 1970, Muhammad Ali (born Cassius Marcellus Clay Jr.), a professional boxer and conscientious objector to the Vietnam War, was convicted for refusing induction into the armed forces. He appealed his conviction on grounds that his religious beliefs were not considered during his draft classification process. The Supreme Court initially upheld this conviction but later reversed it in an 8-0 decision due to procedural errors by the Department of Justice. The court found that there was no basis for denial of conscientious objector status because Ali met all three basic tests: he opposed war based on religious belief; his objection was sincere; and he objected to all wars rather than just one particular conflict.

In the dissenting opinion for Clay, AKA Ali v. United States, Justice Harlan argued that Muhammad Ali's conviction should be upheld because his objection to military service was not based on religious beliefs but rather political and racial objections. He pointed out that the Court had previously ruled in cases such as Gillette v. United States (1971) that conscientious objector status could only be granted if an individual’s opposition to war was rooted in religious belief or training and applied to all wars, not just specific conflicts. In this case, he believed Ali's refusal of military service stemmed from his disagreement with U.S policy regarding Vietnam War and racial issues within America itself - reasons which do not qualify under the legal definition of a conscientious objector according to previous rulings by the court.