the single most important piece of labour legislation enacted in the United States in the 20th century. It was enacted to eliminate employers' interference with the autonomous organization of workers into unions (organized labour).

Sponsored by Senator Robert F. Wagner, a Democrat from New York, the Wagner Act established the federal government as the regulator and ultimate arbiter of labour relations. It set up a permanent, three-member National Labor Relations Board (q.v.; NLRB) with the power to protect the right of most workers (with the notable exception of agricultural and domestic labourers) to organize unions of their own choosing and to encourage collective bargaining. The act prohibited employers from engaging in such unfair labour practices as setting up a company union and firing or otherwise discriminating against workers who organized or joined unions. Under the Wagner Act, the NLRB was given the power to order elections whereby workers could choose which union they wanted to represent them. The act prohibited employers from refusing to bargain with any such union that had been certified by the NLRB as being the choice of a majority of employees.