Overtime Compensation Protection Act of 2003 - Amends the Fair Labor Standards Act of 1938 (FLSA) to prohibit the Secretary of Labor from promulgating any regulation that has the effect of exempting from FLSA overtime compensation requirements (which limit maximum hours at regular compensation) any employee who is not otherwise exempted under regulations in effect on the date of enactment of this Act. Provides that such prohibition does not bar the Secretary from reducing the number of employees who are exempt from such overtime compensation requirements.