While the law says that you have to be paid overtime when worked, there is nothing in the law that says an employer has to allow you to work overtime. Your employer, not you, decides what hours you work, and if your employer wants to rearrange your hours so that you do not work overtime, the law is perfectly fine with that. While Betty is technically correct that a legally binding employment contract could say otherwise, after 35 years in HR I have never seen a contract or union policy that grants the employee the opt of choosing how many hours to work regardless of what the employer wants, and I very much doubt that one exists anywhere, since that would put control outside the hands of those who write the checks and in the hands of those who receive them.