Right or wrong in your eyes the union MUST as a matter of law defend the person in question. It's called "Duty of Fair Representation"
Piney that is one of the reasons I don't like Unions. If they had real leadership unions would get that law changed (they could in a heart beat) and then Police their own. If I ran a Union we would have much higher standards then even the company. That would work much more in the Unions favor come negotiation time then defending the guilty. The unioms shouldn't have to be Public Defenders too!