Final answer:
Secondary action involves unions influencing an employer by pressuring another employer; labor unions use collective bargaining, strikes, work-to-rule campaigns, and picketing to negotiate better conditions for their members.
Step-by-step explanation:
An attempt by a union to influence an employer by putting pressure on another employer, such as a supplier, is known as secondary action. Labor unions are organizations of workers that engage in activities like collective bargaining and strikes to improve wages, working conditions, and benefits for their members.
Unions can also engage in work-to-rule campaigns, where workers strictly follow the rules to slow operations, and picketing, which involves demonstrating at a business site to publicize a labor dispute.