Passage and amendment of the RLA

The RLA was the product of negotiations between the major railroad companies and the unions that represented their employees. Like its predecessors, it relied on boards of adjustment, established by the parties, to resolve labor disputes, with a government-appointed Board of Mediation to attempt to resolve those disputes that board of adjustment could not. The RLA promoted voluntary arbitration as the best method for resolving those disputes that the Board of Mediation could not settle.

Congress strengthened these procedures in the 1934 amendments to the Act, which also prohibited "yellow dog" contracts and created a procedure for resolving whether a union had the support of the majority of employees in a particular "craft or class", while turning the Board of Mediation into a permanent agency, the National Mediation Board, with broader powers.

Congress extended the RLA to cover airline employees in 1936. In 1951 Congress legalized the union shop, which the railway unions had opposed at the time of the original passage of the Act because of the prevalence of employer-dominated company unions at that time.