Union shops are workplaces in which the employees are obligated to join or pay dues to a labor union. Some of the synonyms to describe the union shop include closed shop, agency shop, and union security agreement. The closed shop is a union shop in which only union members are hired, leading to the exclusion of non-union members. An agency shop allows employers to hire non-union members but requires them to pay fees. A union security agreement is a contract that requires employers to support union activities by agreeing to hire only union members. These synonyms have been used to describe workplace environments in which a labor union has significant influence over worker protection, wages, and benefits.