The government protects the right of workers to organize in order to address issues of wages, benefits, and working conditions. The body of laws that protect this right is known as the National Labor Relations Act, sometimes referred to as the Wagner act.
Workers have the right to strike.
Workers have the right to join a union. The Wagner Act prohibits the employer from certain acts, known as unfair labor practices. If you feel you are the victim of an unfair labor practice, contact the NLRB, which will assign an agent to look into your case or consult a lawyer. Threatening a worker in any way, implicitly or explicitly, because of union activities. This can include demotions, reprimands, etc.