What piece of u. s legislation acts as the primary authority on collective bargaining

The main body of law governing collective bargaining is the National Labor Relations Act (NLRA). It is also referred to as the Wagner Act. It explicitly grants employees the right to collectively bargain and join trade unions. The NLRA was originally enacted by Congress in 1935 under its power to regulate interstate commerce under the Commerce Clause in Article I, Section 8 of the U.S. Constitution. It applies to most private non-agricultural employees and employers engaged in some aspect of interstate commerce. Decisions and regulations of the National Labor Relations Board (NLRB), which was established by the NLRA, greatly supplement and define the provisions of the act.

The NLRA establishes procedures for the selection of a labor organization to represent a unit of employees in collective bargaining. The act prohibits employers from interfering with this selection. The NLRA requires the employer to bargain with the appointed representative of its employees. It does not require either side to agree to a proposal or make concessions but does establish procedural guidelines on good faith bargaining. Proposals which would violate the NLRA or other laws may not be subject to collective bargaining. The NLRA also establishes regulations on what tactics (e.g. strikes, lock-outs, picketing) each side may employ to further their bargaining objectives.

State laws further regulate collective bargaining and make collective agreements enforceable under state law. They may also provide guidelines for those employers and employees not covered by the NLRA, such as agricultural laborers.

Iwould say the answer is 4.