Legal Question in Employment Law in Illinois

Your work hours are a "condition of employment". In a union shop, management would have to negotiate with your union rep to effect the change. In a non-union shop, you are working at the will of your supervisor. You should try to negotiate a pay bump in exchange for the inconvenience of a change in hours. If you can't accept the change, you may be eligible for unemployment compensation by virtue of an involuntary termination due to a change in working conditions. The best course of action may be to accept the change and start looking for a new job!