5 USC 3524 - Effect of subsequent employment with the Government

(a) The term employment
(1) in subsection (b) includes employment under a personal services contract (or other direct contract) with the United States Government (other than an entity in the legislative branch); and
(2) in subsection (c) does not include employment under such a contract.
(b) An individual who has received a voluntary separation incentive payment under this subchapter and accepts any employment for compensation with the Government of the United States with[1] 5 years after the date of the separation on which the payment is based shall be required to pay, before the individuals first day of employment, the entire amount of the incentive payment to the agency that paid the incentive payment.
(c) 
(1) If the employment under this section is with an agency, other than the Government Accountability Office, the United States Postal Service, or the Postal Regulatory Commission, the Director of the Office of Personnel Management may, at the request of the head of the agency, may[2] waive the repayment if
(A) the individual involved possesses unique abilities and is the only qualified applicant available for the position; or
(B) in case of an emergency involving a direct threat to life or property, the individual
(i) has skills directly related to resolving the emergency; and
(ii) will serve on a temporary basis only so long as that individuals services are made necessary by the emergency.
(2) If the employment under this section is with an entity in the legislative branch, the head of the entity or the appointing official may waive the repayment if the individual involved possesses unique abilities and is the only qualified applicant available for the position.
(3) If the employment under this section is with the judicial branch, the Director of the Administrative Office of the United States Courts may waive the repayment if the individual involved possesses unique abilities and is the only qualified applicant available for the position.
[1] So in original. Probably should be “within”.
[2] So in original.