mandatory OT?!?

Well this is a first for me, thought I might see if you have heard of this(or any advice). I accepted a contract in CT (I am from IL), got here two weeks ago and everything has been going well until this past weekend. I was working a 12 hour night shift on Friday night, at 0330 I was informed I was being mandated to work overtime due to emergency staffing. I questioned the house supervisor about it, there is nothing with in my contract that says I can be mandated, I never agreed to any kind of mandatory staffing. HS tells me that it is with in the contract between the hospital/agency. Three of us night shift nurses all had to take a four hour increments. Someone 7-11, another 11-3 and then 3-7/ All three of us had to return to work at 7pm Saturday. They wanted me to work 7am-11am the following Saturday morning. I needed to get back to my housing (30 minutes away) due to some obligations I had. I traded another nurse, so I ended up working the 3-7 slot. Before I reported to work at 3, I called the HS to make sure I was still needed...she informed me I was so that they could safetly have somewhere to admit to. (seriously is that emergent staffing???) I watched a staff nurse work 12 hour nights, be off four hours, work four hours, off four and then return to work another 12. I have never seen anything like it before in my life. The staff nurses here tell me that this happens frequently on the weekends. I called the agency this morning to inform them of the above, and that I would NOT be working 12, off 4, work 4 off 4 and work another 12. I couldnt even see straight if I tried to do that. They contacted the hospital and the assistant nurse manager called me this morning....and says that is with in their union contract to help with emergency staffing. I told her I was not in the union... I said it would not be safe for me to even drive under those conditions...the assistant nurse manager tells me that I can sleep in the hospital. Now if I am not safe to drive..why would I be safe to practice as a critical care nurse? I have a strong feeling this contract is going to be cancelled tomorrow. Anyone experience anything like this before? Would appreciate any advice/feedback that you have. Thanks
Also since when does a poorly staffed schedule become an emergency? IMO an emergency is something that wasnt expected...not a schedule that has been out a month and no one signed up to work it! The managers lack of planning...doesnt become my emergency!