5 U.S.C. § 6127

1. (a)Notwithstanding section 6101 of this title, each agency may establish programs which use a 4-day workweek or other compressed schedule.
2. (b)
   1. (1)An employee in a unit with respect to which an organization of Government employees has not been accorded exclusive recognition shall not be required to participate in any program under subsection (a) unless a majority of the employees in such unit who, but for this paragraph, would be included in such program have voted to be so included.
   2. (2)Upon written request to any agency by an employee, the agency, if it determines that participation in a program under subsection (a) would impose a personal hardship on such employee, shall—A determination by an agency under this paragraph shall be made not later than 10 days after the day on which a written request for such determination is received by the agency.
      1. (A)except such employee from such program; or
      2. (B)reassign such employee to the first position within the agency—
         1. (i)which becomes vacant after such determination,
         2. (ii)which is not included within such program,
         3. (iii)for which such employee is qualified, and
         4. (iv)which is acceptable to the employee.