You have to know your right and ask to use it. Once you've asked for the steward, any attempt by management to continue asking questions before a steward gets there is illegal. If this discussion could in any way lead to my being disciplined or terminated, or affect my personal working conditions, I request that my union representative, officer, or steward be present at the meeting. Without representation, I choose not to answer any questions. The steward can serve as a witness to prevent supervisors from giving a false account of the conversation.
Many people find it hard to talk under pressure.
The steward can help you explain things. If you're hot headed, the steward can help you keep cool. Stewards have often dealt with similar situations before and can help you figure out what you should and shouldn't say. You do have to answer the questions, but stewards can help you figure out the best way to do so. They can also provide information to management after the questioning is over that can help explain your situation.