In the case of McGinnis, Commissioner of Correction, et al. v. Royster et al., 1972, the U.S Supreme Court addressed whether New York's system for awarding good time credits to prisoners violated equal protection principles under the Fourteenth Amendment. The state’s policy allowed inmates serving shorter sentences to earn fewer good time credits than those serving longer sentences. A group of inmates challenged this policy arguing that it discriminated against them based on their sentence length and thus was unconstitutional. The Supreme Court upheld New York's system in a 5-4 decision stating that there was no violation of equal protection rights as there were rational reasons behind such differentiation - mainly focusing on rehabilitation and maintaining prison discipline. The court reasoned that prisoners with longer sentences had more need for incentives to maintain good behavior over an extended period while also requiring more time for effective rehabilitation before release back into society.

In the dissenting opinion for McGinnis v. Royster, Justice Thurgood Marshall argued that the majority failed to consider the discriminatory impact of New York's good time allowance system on pretrial detainees. He contended that this system violated equal protection by giving more generous sentence reductions to convicted prisoners than to those awaiting trial who could not afford bail. According to him, it was unjustifiable and arbitrary discrimination against poor defendants since they were denied an opportunity for a shorter sentence simply because they couldn't post bail before their trials began. Furthermore, he believed that such a policy did not serve any legitimate state interest in punishment or rehabilitation but rather perpetuated socioeconomic inequality within the criminal justice system.