Seasonal change of hours

Confused1aaa

Manager in a factory, always very busy in the run up to Christmas, managers are usually required to help out on the factory floor and work on the floor for the 2 weeks before Christmas and this usually means a few extra hours and or working 6 days. But this year they are taking advantage, I’ve been told I’m working 3pm to 3 am from next week until the 23rd, 5 or 7 days a week depending on how busy we are, not supervising like the other managers but working on the production floor. I’m paid salary so am expected to do up to 168 hours for the same money- no time in lieu, no bonus etc etc.

My question is how to approach saying no and refusing to do this without souring my relationship with work