5 U.S.C. § 3405

1. (a)If, on the date of enactment of this chapter, there is in effect with respect to positions within an agency a collective-bargaining agreement which establishes the number of hours of employment a week, then this chapter shall not apply to those positions.
2. (b)This chapter shall not require part-time career employment in positions the rate of basic pay for which is fixed at a rate equal to or greater than the minimum rate payable under section 5376.