The Supreme Court case Plessy v. Ferguson arose from an incident in 1892 when Homer Plessy, who was one-eighth Black, sat in a 'whites-only' passenger car of a Louisiana train and was arrested for violating state segregation laws. Plessy challenged the law in court, contending that it infringed upon his rights under the 14th Amendment, which guarantees equal protection under the law. The case ultimately reached the Supreme Court, where the justices handed down a 7-1 decision in 1896, authored by Justice Henry Billings Brown. The ruling established the 'separate but equal' doctrine, which stated that if separate facilities for the races were equal, segregation did not violate the Constitution. This ruling provided legal justification for racial segregation across various public facilities in the United States, including schools, transportation, and restrooms.

The dissenting opinion, expressed by Justice John Marshall Harlan, starkly criticized the majority's ruling, arguing that it was a betrayal of the principles of freedom and equality. Harlan famously predicted that the decision would become as infamous as the Dred Scott decision. Despite this dissent, the ruling reinforced the legality of racial segregation, paving the way for Jim Crow laws that institutionalized discrimination against African Americans for decades to come. Thus, the Plessy case marked a significant moment in the legal acceptance of racial discrimination.