The Taft-Hartley Act (also known as the Labor-Management Relations Act) was passed over the veto of Harry S. Truman on 23rd June, 1947. When it was passed by Congress Truman denounced it as a "slave-labor bill".
The act declared the closed shop illegal and permitted the union shop only after a vote of a majority of the employees. It also forbade jurisdictional strikes and secondary boycotts. Other aspects of the legislation included the right of employers to be exempted from bargaining with unions unless they wished to.
The act forbade unions from contributing to political campaigns and required union leaders to affirm they were not supporters of the Communist Party. This aspect of the act was upheld by the Supreme Court on 8th May, 1950.
The Taft-Hartley Act also gave the United States Attorney General the power to obtain an 80 day injunction when a threatened or actual strike that he/she believed "imperiled the national health or safety".