In 1975 the United States Supreme Court, in the case of NLRB v. J. Weingarten, Inc., 420 U.S. 251 (1975), upheld a NLRB decision that employees have a right to union representation at investigatory interviews. These rights have become known as the Weingarten Rights.
During an investigatory interview by an employer the Supreme Court ruled that the following rules apply:
RULE 1: The employee must make a clear request for union representation before or during the interview. The employee cannot be punished for making this request.
RULE 2: After the employee makes the request, the employer must choose from among three options. The Employer must either: grant the request and delay questioning until the union representative arrives and has a chance to consult privately with the employee; deny the request and end the interview immediately; or give the employee a choice of having the interview without representation or ending the interview.
RULE 3: If the employer denies the request for union representation, and continues to ask questions, it commits an unfair labor practice and the employee has a right to refuse to answer. The employer may not discipline the employee for such a refusal.
Visit the below links to learn the history of your Weingarten Rights.
Click the below link for a handy Weingarten Rights card you may carry with you - it details what you must say to request the presence of a union representative during questioning.