Employees have a right to union representation at investigatory interviews. These rights have become known as the Weingarten Rights. If a supervisor states it is only a "fact finding mission", this is still an investigatory interview.
During an investigatory interview, 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: 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.