Union security provisions generally refer to those clauses of a labor contract which protect the union’s status under the agreement. Such contract clauses are not compelled under the law, but they are allowed to be negotiated between an employer and a union. They bind individual employees only when an agreement is reached between a worker’s employer and union.

Unions will not often acknowledge that they lobbied for and ultimately won the right of exclusive representation.

Union security provisions are frequently classified as either open shop, agency shop or union shop. An open shop exists when there is no union security clause. The agency shop, common in government employment, does not require union membership but does require the payment of a union representation or service fee. The union shop requires union membership in good standing for continued employment.

A union shop requires employees to join the union within a specified period of time and remain members "in good standing." Thus, an employee need not be a member of the union to be hired. (The so-called closed shop, which required an employee to be a member of the union in order to be hired, was outlawed by the enactment of the Taft-Hartley amendments in 1947.) As a condition of continued employment, however, the employee must join the union within a designated period—30 days for industry generally, 60 days for railroad and airline employees, and 7 days for construction work. Under the law, the requirement to "join a union" and to remain a member "in good standing" under a union shop clause has largely meant that the employee must tender regular dues and initiation fees.

An employee who refuses to voluntarily join the union or to pay dues under a union security agreement must be discharged upon the union’s request to the employer. Nonetheless, an employee who offers to pay dues and the appropriate fees but is denied union membership for any reason has satisfied the prerequisites of the law under a union shop proviso. Such an employee cannot be discharged because of his or her non-membership in the union.

The Supreme Court in NLRB v General Motors Corp. defined the extent of union membership that could be required under the NLRA’s authorized union shop agreements. 12  The Court held that the law in Section 8(a)(3), allowing the employer and the union to condition continued employment of the employee on union membership, was limited to requiring the payment of union membership fees. 13  Thus an employee who pays union fees as a nonmember is entitled to keep his or her job as if he or she were a full member. So long as union fees are paid, the employee cannot be discharged for any other union-imposed obligation. 14  The only obligation for membership that can be placed upon an employee under Section 8(a)(3) is financial membership. The Court held that the term "membership" is, at its core, financial support of a union. 15 

The union shop agreement is an exception to the freedom granted an employee under the NLRA, Section 8(a), to join or not join a labor organization. Adoption of the union shop between an employer and a union is made subject to state law under Section 14(b) of the Taft-Hartley amendments of 1947. Thus the union shop, the agency shop, and other forms of union security provisions are lawful, provided that they are not prohibited by state statute. Twenty-one states, mostly in the South and West, have enacted laws prohibiting labor agreements that compel union membership. 16  States with such laws are commonly referred to as right-to-work states. Michigan is not a right-to-work state.

Unions justify imposing mandatory financial burdens on all workers, whether members or not, on the theory that unions must represent all workers in the bargaining unit by law. Therefore, the protections and benefits the union negotiates benefit all, and it is only fair that each employee pay for the costs of this representation. This is the so-called "free rider" argument.

Unions will not often acknowledge that they lobbied for and ultimately won the right of exclusive representation. This is an important institutional goal because it immunizes the labor movement from competition from other organizations and persons desiring to become workplace employee agents. Without exclusive representation, there could be no free riders because employees would retain the choice of whether to be represented or not. The burdens unions claim resulting from exclusive representation ring hollow in light of their overriding institutional interests to be free from competition. Forced dues payments are equally likely to catch so-called "free riders" as "forced riders"—those employees whose individual interests are sacrificed for the sake of the collective good. "Forced rider" workers are compelled to subsidize union activity and contribute to policies and decisions that they may find harmful.