Solidarity action (also known as secondary action, a secondary boycott, a solidarity strike, or a sympathy strike) is industrial action by a trade union in support of a strike initiated by workers in a separate corporation, but often the same enterprise, group of companies, or connected firm.

In Australia, Latvia, Luxembourg, the Netherlands, the United States, and the United Kingdom, solidarity action is illegal, and strikes can only be against the contractual employer. Germany, Italy and Spain have restrictions in place that restrict the circumstances in which solidarity action can take place (see European labour law).

The term "secondary action" is often used with the intention of distinguishing different types of trade dispute with a worker's direct contractual employer. Thus, a secondary action is a dispute with the employer's parent company, its suppliers, financiers, contracting parties, or any other employer in another industry.