In the case of Plessy v. Ferguson what did Homer Plessy refuse to do?

In the case of Plessy v. Ferguson, Homer Plessy refused to leave a "whites-only" railroad car in Louisiana. He was of mixed race and his act of defiance was a deliberate challenge to the state's segregation laws. His arrest led to a landmark Supreme Court case in 1896, which ultimately upheld the constitutionality of racial segregation under the "separate but equal" doctrine.