he's full of **** as far as seniority goes. If junior employees are taking work from you (hours), warn them, and if they don't correct it, file on it. Remember the date and time you warned them though for ammo on the greivance.
I know in the reload shift, just as an unloader/loader those aren't bid jobs. They can move you to the air station, loading trailers, unloading trailers and unloading package cars as they please. However, seniority rules as far as start time and who is getting more work (inlcuding OT).