In the 1945 case Robertson v. California, the U.S. Supreme Court ruled on a dispute involving labor law and collective bargaining rights for agricultural workers in California. The plaintiff, Robertson, was an agricultural worker who challenged a state statute that prohibited non-union members from negotiating employment contracts with employers who had already entered into agreements with unions representing their employees. He argued that this restriction violated his constitutional right to freedom of contract under the Fourteenth Amendment's Due Process Clause. The Supreme Court disagreed and upheld the constitutionality of the statute by a vote of 6-3. The majority opinion held that states have broad authority to regulate economic activity within their borders and can restrict individual contractual freedoms when doing so serves legitimate public interests such as promoting industrial peace or preventing labor disputes. This decision affirmed states' power to enact laws favoring unionized over non-unionized workers in certain circumstances, even if these laws limit some individuals' ability to negotiate employment terms independently.

The dissenting opinion in the case of Robertson v. California argued that the majority's decision to uphold a state law requiring union membership as a condition for employment was an infringement on individual liberties. The dissenters contended that compulsory unionism violated freedom of association, which they viewed as inherent in First Amendment rights. They believed this requirement could lead to coercion and intimidation tactics by unions, potentially infringing upon workers' rights to choose whether or not to join such organizations freely. Furthermore, they expressed concern about potential abuses of power by labor unions and suggested that mandatory membership might unduly empower these groups at the expense of individual workers' freedoms and interests.