Thanks for your clarification. My wife has faced the exact same situation at a hospital that she worked at for a long time. I certainly empathize with the situation that you are facing.
As a nurse, I am sure that you are aware that you are an employee at will. That means that you can be let go for any reason so long as that reason is not illegal---such as discrimination based on your race, color, sex etc.
If the employer wants you to work double shifts, there is nothing that you can do to prevent them from asking you to work over when they need it. And while you can certainly refuse, you risk your position with the employer in doing that because they can terminate you if you refuse to take on extra work. Obviously, you must be paid for your time, but yes, they can demand that you work overtime. Their request is perfectly legal and as far as options go, you have no legal options--just options to file a formal complaint that you have through your HR department.
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I wish you and yours the best in 2016,