Was Plessy v Ferguson a federal or state case?

Plessy v. Ferguson, 163 US 537 (1896)

Both. Plessy v. Ferguson began in Louisiana state courts because it involved violation of the Louisiana Separate Car Act of 1890 (Act 111); however, the case was appealed to the US Supreme Court on a federal questionchallenging the constitutionality of the state law.