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.