On probation the only thing you don't have a right to is the grievance process for termination. Everything else in the contract applies to you.
This whole thing the union can't do anything for you or your new so you have no rights is BS. The union can do everything for a probationary member that an active member is entitled to except to grieve a termination.
Anyway it really doesn't apply in this case. He was asked to do something against the FAR's. If you are active, probationary, or don't even have a union at all, there was only ONE simple answer...No.