Yes, they can refuse the note: the doctor's note has no authority over your employer. (It is a common misconception to think that it does.)Furthermore, overtime is 100% under the control of the employer: they have complete discretion to decide who gets overtime, when, and how much.Finally, company policies not incorporarted into a written contract are subject to change at will, so even if they formerly accepted such notes, they may decide now to not do so.Therefore, based on what you write, they do not have to accept the note and may deny you overtime.(The exception to the above: if there is a contract, including a union agreement, which covers overtime and this situation, whatever it says on the subject will control. If there is a contract, you have to review *exactly* what it says about this.)