No, the Plessy v. Ferguson case did not directly challenge the legislative branch. Instead, it was a challenge to the segregation laws enforced by state governments in the Southern United States. The case focused on the constitutionality of a Louisiana law requiring racial segregation in public transportation. The Supreme Court's ruling in Plessy v. Ferguson in 1896 upheld the constitutionality of "separate but equal" facilities, thereby endorsing segregation. So, it was more of a challenge to the executive branch (specifically state governments) and the interpretation of the Constitution by the judiciary.
