Work related

What do you do when you are a new employee and feel your being the target? Senior staff are mad they feel the new staff are getting the better shifts and I'm the middle of 3 new hires and the only one not related to others in the company. I'm still under probation and it's a unionized hospital.  My words are being twisted largely. I have s meeting tomorrow with the boss.. What am I suppose to do? It's he said she said and I'm new