Yellowdog contracts are also known as "ironclad agreements" or "closed shop agreements." These contracts are commonly used in the workplace to restrict employees' ability to join labor unions or engage in collective bargaining. Another term for yellowdog contracts is "yellow-dog provisions," which refers to a specific clause in the contract that prohibits employees from participating in union activities. Some synonyms for yellowdog contracts include "union-busting contracts," "restrictive agreements," and "anti-union contracts." Yellow-dog contracts were deemed illegal by the United States Supreme Court in 1932 but have since been legalized in some states. Many view these contracts as a violation of workers' rights and an attempt to suppress union activity.