Under your negotiated agreement and the law, employees have certain rights and obligations. If you are called into a meeting about everyday work-related events, your rights are probably not affected.
If the meeting with your supervisor requires you to answer questions about some incident or situation, and you reasonably believe you could or will be disciplined as a result, then your rights do come into play.
The employer has the right to conduct an investigation when situations arise. The law requires a fair investigation. As an employee, you have the obligation to obey the employer’s rules and cooperate in an investigation.
If you are called into a meeting and your supervisor asks questions as part of an investigation, you have the right to have another employee attend the meeting with you as a witness. It is your responsibility to tell your supervisor you want to have another person in that meeting as your witness. Generally, the supervisor is not obligated to tell you unless there is specific language to that effect in your contract. The person is there to take notes and to ask clarifying questions.
You should answer all questions truthfully. If there is some indication that you are involved in a criminal matter, it is best not to answer any questions that might incriminate you in any way. You will want to consult with an attorney first before answering questions if it is a criminal matter.