What should have happened or maybe what the rep should/could have done.
Ask for information pertaining to the last 12 month work history of that Depot for all overtime, cover required for each Saturday/Monday and Tuesday.
This will tell you very clearly on how the D.O & business managed on those days including showing any seasonal variances.
Let's just say the information was to hand by RM and indeed it showed very little being paid extra on those days due to a reduced inbound work volume, then that is how the conversation should have gone. The members at the DO could have discussed it but would in fact have little to argue against it and maybe would have agreed to such moves to protect jobs.
Instead RM have provided no information other than 'This is going to happen'
When will they learn that transparency in the initial aspect can remove a lot of unnecessary steps in causing more stress / anguish to members.
So to the OP, maybe the rep can get hold of this information to share with you ?