The agency is supposed to notify the union of an imbalance. This is the benefit to collaboration, being able to have this discussion between the parties. They don’t get to unilaterally just make decisions.
Yes if certain days are busier they could say they need more bodies there, but that would have needed to be discussed during BWS negotiations.
The key point to this is that the trainee owns those RDO’s with no strings attached if there isn’t an imbalance. Many facilities do this incorrectly.
If you have 7 crews of 3 cpcs and now with this newly certified dev, you have a crew with 4. They don’t move, there’s no imbalance. Tough shit, move on.