5 U.S.C. § 5524a

(a) (1) The head of each agency may provide for the advance payment of basic pay, covering not more than 2 pay periods, to any individual who is newly appointed to a position in the agency. (2) The head of each agency may provide for the advance payment of basic pay, covering not more than 4 pay periods, to an employee who is assigned to a position in the agency that is located— (A) outside of the employee’s commuting area; and (B) in the United States, the Commonwealth of Puerto Rico, the Commonwealth of the Northern Mariana Islands, or any territory or possession of the United States. (b) (1) Subject to adjustment of the account of an employee under paragraph (2) and other applicable statutes, the advance payment of basic pay shall be made, under agency procedures governing advance payments under this section, at the initial rate of basic pay to be payable to the employee upon the commencement of service in the position to which appointed or assigned. (2) The head of each agency shall provide for— (A) the review of the account of each employee of the agency in receipt of any payment under this section; and (B) the adjustment of the amount of any such payment on the basis of the rate of basic pay to which the employee would have been entitled under applicable statute other than this section for the respective periods covered by the payments, if the employee had performed active service under the terms of such employee’s appointment or assignment during each period in the position to which appointed or assigned. (c) An advance payment under this section is recoverable by the Government of the United States or the government of the District of Columbia, as the case may be, from the employee or such employee’s estate by— (1) setoff against accrued pay, amount of retirement credit, or other amount due to the employee from the Government of the United States or the government of the District of Columbia; and (2) such other method as is provided by law. The head of the agency concerned may waive in whole or in part a right of recovery of an advance payment under this section if it is shown that the recovery would be against equity and good conscience or against the public interest.