Final answer:
The first federal law pertaining to labor relations was the Wagner Act or National Labor Relations Act, enacted in 1935 to protect workers' rights to unionize and bargain collectively, and established the NLRB.
Step-by-step explanation:
The first federal law pertaining to labor relations was the Wagner Act, also known as the National Labor Relations Act. It was enacted in 1935 as part of President Roosevelt's Second New Deal. The Wagner Act reinstated the principle of government support for workers' rights to join unions and bargain collectively after the National Industrial Recovery Act (NIRA) provisions were lost when the Supreme Court declared NIRA unconstitutional.
It prohibited discrimination against union members and mandated employer recognition of a union if the majority of their workers were members. This act also established the National Labor Relations Board (NLRB) to enforce its provisions and arbitrate disagreements between unions and employers, marking a significant step forward in U.S. labor relations.