So how do you know when to ask for representation? Let's go through a hypothetical situation. You get a note from your supervisor saying, "See me on your break." When you show up fore the meeting, your first question should be, "Is this meeting of a disciplinary nature or could it be?" If the answer is, "Yes," then you should ask for representation. If the answer is, "Maybe, " or "That depends," then you should ask for representation. If the answer is, "No," you should remember that if you feel like the meeting is taking a disciplinary turn that you should ask for representation.
If the supervisor denies you representation, then your rights have been violated, but you must not be insubordinate. You should respond to questions with, "I'll be happy to respond to that when I have representation." If the supervisor threatens you with insubordination, you should respond, but know that anything that comes from that meeting cannot be used against you.
Always remember that if you feel like you are going into a meeting that could be disciplinary in nature, you should ask for union representation.