About the only possible recourse this person would have, if he were terminated, would be to file for unemployment insurance. And in the decision whether or not he receives unemployment insurance after his termination, it does matter if he refused to cooperate with management.
I'm in favor of a "signing this disciplinary notice to cooperate with management, but not in any way agreeing to or admitting the wrongdoing herein mentioned" statement written in. But there's no law in place about signing or not signing a disciplinary notice, because there are very few labor laws about what they can and can't fire your for, because as we've pointed out to you, they could fire you for just about anything.
If they cannot prove that they had a good job related reason to terminate you, then you probably will be able to receive unemployment benefits when terminated. But if your father's union is not going to help him grieve this disciplinary action, he really doesn't have much recourse. They probably will not fire him. He should keep written notes concerning what he has been told by those other people. If he is terminated or falsely accused by her again, they might come in handy.
Thanks for your advice.
