Clocked this today after being told about it and i couldn't believe it!

Seething here as if swapping holidays wasn't hard enough he's now trying to make it impossible as i'm an AG (well 36 hrs so not far off fulltime)
Last i heard was the Union was not happy about this and will be looking to have a chat with the DOM regards the matter when he's back in work - he's now off till Mon
Can the DOM even do this? discrimination if you ask me against the AG staff.
Thoughts?