Yellow-dog contract
A yellow-dog contract (a yellow-dog clause of a contract, or an ironclad oath) is an agreement between an employer and an employee. The employee agrees not to be a part of a trade union. This was part of a contract which employers and employees signed when employees were hired. In the United States, yellow-dog contracts or yellow-dog clauses were often used by employers to stop the creation of unions. It let employers take legal action against union organizers.  In 1932, yellow-dog contracts were made illegal in the United States under the Norris-LaGuardia Act.