The case of Police Department of the City of Chicago et al. v. Mosley in 1971 involved a city ordinance that prohibited picketing or demonstrations near schools, except for peaceful labor picketing. Earl Mosley, a non-union school employee, challenged this rule after he was barred from peacefully protesting against racial discrimination at his workplace - a school. The Supreme Court ruled unanimously in favor of Mosley on First Amendment grounds stating that the government cannot discriminate between lawful and unlawful peaceful picketing based on subject matter or content alone unless it can show that its regulation is necessary to serve a compelling state interest and is narrowly drawn to achieve that end.

In the dissenting opinion for Police Department of the City of Chicago et al. v. Mosley, Justice Black argued that the ordinance in question was not a violation of equal protection under law because it did not discriminate against any particular group or individual based on race, religion, or other protected characteristics. Instead, he believed that it was a reasonable regulation by local government to maintain peace and order around schools during operating hours. He also disagreed with the majority's view that this case involved content-based discrimination since both labor picketing and peaceful protests were treated differently under different circumstances elsewhere in Illinois law without violating free speech rights. Furthermore, he contended that if all forms of picketing were allowed near schools as per First Amendment rights then there would be no end to disturbances which could disrupt education.