In the 1949 case of International Union of United Automobile, etc. Workers of America, C.I.O., et al. v. O'Brien, Prosecuting Attorney, et al., the U.S Supreme Court ruled on a dispute involving labor unions and their right to picket peacefully during strikes without interference from state law enforcement officials in Michigan. The court held that peaceful picketing was protected by the First Amendment's guarantee of freedom of speech and could not be prohibited or restricted by state laws unless it involved violence or intimidation tactics that threatened public order or safety. This ruling reaffirmed previous decisions recognizing labor unions' constitutional rights to express their grievances publicly through peaceful demonstrations and protests.

In the dissenting opinion for International Union of United Automobile, Etc. Workers of America, C.I.O., et al. v. O'Brien, Prosecuting Attorney, et al., Justice Black argued that the majority's decision to uphold Michigan's anti-strike law violated workers' First Amendment rights to free speech and assembly. He contended that strikes are a form of protest and communication used by labor unions to express their grievances and negotiate better working conditions with employers - thus they should be protected under the Constitution as an essential part of democratic society. Furthermore, he criticized the majority for interpreting too broadly states' power to regulate economic activities in ways that infringe upon fundamental civil liberties.