What is it called when management prevents union members from working during a dispute?

The situation described occurs when management implements a lockout. A lockout is a work stoppage initiated by an employer during a labor dispute, where the employer prevents union members from working in order to force negotiations or changes in behavior from the union. This tactic is often used as a response to a strike initiated by workers, but it primarily serves to demonstrate management's power and willingness to halt operations in order to negotiate better terms or conditions.

In contrast, a strike refers to the action taken by workers when they refuse to work as a means to exert pressure for better conditions or pay. Picketing typically involves workers standing outside a location to protest or bring attention to their cause but does not involve stopping work by the employer. A boycott, on the other hand, is a refusal to purchase goods or services from a company, intended to force a change in business practices, but it does not directly involve the employment situation like a lockout does. Thus, the definition and function of a lockout clearly distinguish it as the correct answer.