I truly wonder when the folks at ALPA will wake up properly, and discover the present day scenario at many airline companies....do as you are told, or face the consequences.
Atlas has every right to transfer aircraft between the two companies, and I am certainly not totally surprised that ALPA has dropped the ball here, and not realized before that the upper hand in this scenario, as with nearly EVERY airline company, is held by the airline management.
Co-operate and graduate, or be shown the door.
True in the distant past? No, but certainly true now.
CX pilots found out first hand, much to their disappointment, I'm sure.