Dear SusieB -   The answer to what your employer can require here depends on what exactly you are asking for.  I'm not clear on whether you are asking for accommodations under the ADA, See Working with Migraines: Rights Under the Americans with Disabilities Act, in order to make it possible for you to continue to perform the job, or whether you have Family Medical Leave Act (FMLA) status, allowing you 90 days of unpaid time off per year, or whether you are seeking some other kind of partial disability status offered by the military.   In general a medical exam is not required to request an accommodation under the ADA, but employers are not required to grant a specific accommodation (they can eveluate your request and offer an alternative), and there is a fair amount of flexibility granted to them under the law.  The EEOC's ADA guidelines state:           "Employers may conduct employee medical exams where there is evidence         of a job performance or safety problem, examinations required by Federal         laws, examinations to determine current fitness to perform a particular job,         and voluntary examinations that are part of employee health programs." Americans with Disabilities Act Questions and Answers. Is the exam they want to conduct required by Federal law, or necessary to determine your fitness to perform your job? If so, they can probably require it.     Under the FMLA, on the other hand, your employer can require second and third opinions (paid for by the employer) of your disability or medical condition, and periodic re-examinations to determine if you are still entitled to leave.   If this is some other type of medical or partial disability leave offered you through the military there must be rules for the particular type of leave which would govern.   Good luck to you!   - Megan