In the case of Carlson v. California, 1939, the United States Supreme Court ruled that a California law prohibiting picketing was unconstitutional as it violated the First Amendment rights to freedom of speech and assembly. The appellant, Mr. Carlson had been convicted under this state law for peacefully picketing with signs expressing labor disputes in front of a business establishment in Los Angeles County. He argued that his conviction infringed upon his constitutional rights to free expression and peaceful assembly protected by the Fourteenth Amendment's due process clause which extends federal constitutional protections to states' actions. The Supreme Court agreed with him and reversed his conviction on grounds that such blanket prohibition against all forms of picketing is an unreasonable restriction on liberty of discussion without sufficient justification or compelling interest from government side.

In the dissenting opinion for Carlson v. California, Justice McReynolds argued that the majority's decision to strike down a California law prohibiting picketing was incorrect. He contended that states should have the right to regulate or prohibit certain types of speech and assembly in order to maintain public order and safety. According to him, this power is not limited by the First Amendment as it applies only against federal laws, not state ones due to its wording which says "Congress shall make no law". Furthermore, he believed that peaceful picketing could easily turn into intimidation or violence hence justifying regulation by states. Lastly, he pointed out that many other countries also limit freedom of speech and assembly in similar ways without infringing on basic human rights.