The general rule of employment is: At-Will. Meaning, among other things, in the absence of a contract or illegal motive, an employer need not give any notice offer chages in shifts, availability of shifts, termination, pay changes, etc. Refusal to accept employment or quitting a job without good cause could jeopardize unemployment compensation insurance eligibility. Check with your state's agency.
Kindly note and remember that my response is merely a general comment on the law related to your question, and NOT legal advice or opinion. Also, your question and my response does NOT create an attorney-client relationship between us. You cannot rely upon what I have written, because I do not have all of the information that I need to advise you or render an opinion. Even simple facts you have not shared can completely change my answer. For me to give you legal advice or opinion, you would need to hire me to be your lawyer, and then we would need to discuss this in detail and go over the documents.
IRS CIRCULAR 230 DISCLOSURE: As required by U.S. Treasury Regulations governing tax practice, you are hereby advised that written advice contained herein (if any) was not written or intended to be used (and cannot be used) by any taxpayer for the purpose of avoiding penalties that may be imposed under the U.S. Internal Revenue Code.