(a)(1)     In the case of employees in a unit represented by an exclusive representative, any flexible or compressed work schedule, and the establishment and termination of any such schedule, shall be subject to the provisions of this subchapter and the terms of a collective bargaining agreement between the agency and the exclusive representative.

        (2)     Employees within a unit represented by an exclusive representative shall not be included within any program under this subchapter except to the extent expressly provided under a collective bargaining agreement between the agency and the exclusive representative.

  (b)     An agency may not participate in a flexible or compressed schedule program under a collective bargaining agreement which contains premium pay provisions which are inconsistent with the provisions of section 6123 or 6128 of this title, as applicable.