Unless your employment is already covered by a written contract or agreement (for example, a collective bargaining agreement), your employer has the right to set your work hours, and your continued employment would likely be deemed acceptance to the new terms. Unfortunately, there is probably nothing you can do about your situation other than go along with it or find a new job. Good luck to you.
Not unless there is an express written or other agreement otherwise.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.