They're obligated to represent him by attending management/arbitration meetings with/for him. That's not to say they'll actually speak. I've seen union reps sit with their arms folded and mouths firmly slammed shut while the member gets sliced and diced for an indefensable violation. It's rare and it's usually a call from the national union office "ivory tower",but,it happens when the Union can be brought into a PR disaster and literally backed into a dark corner. This may be one of those times.