5 U.S.C. § 5728

(a) Under regulations prescribed under section 5738 of this title , an agency shall pay from its appropriations the expenses of round-trip travel of an employee, and the transportation of his immediate family, but not household goods, from his post of duty outside the continental United States, Alaska, and Hawaii to the place of his actual residence at the time of appointment or transfer to the post of duty, after he has satisfactorily completed an agreed period of service outside the continental United States, Alaska, and Hawaii and is returning to his actual place of residence to take leave before serving another tour of duty at the same or another post of duty outside the continental United States, Alaska, and Hawaii under a new written agreement made before departing from the post of duty. (b) Under regulations prescribed under section 5738 of this title , an agency shall pay from its appropriations the expenses of round-trip travel of an employee of the Government appointed by the President, by and with the advice and consent of the Senate, for a term fixed by statute, and of transportation of his immediate family, but not household goods, from his post of duty outside the continental United States, Alaska, and Hawaii to the place of his actual residence at the time of appointment to the post of duty, after he has satisfactorily completed each 2 years of service outside the continental United States, Alaska, and Hawaii and is returning to his actual place of residence to take leave before serving at least 2 more years of duty outside the continental United States, Alaska, and Hawaii. (c) (1) Under regulations prescribed under section 5738 of this title , an agency may pay, subject to paragraph (3) of this subsection, the expenses described in paragraph (2) of this subsection in any case in which the head of the agency determines that the payment of such expenses is necessary for the purpose of recruiting or retaining an employee for service of a tour of duty at a post of duty in Alaska or Hawaii. (2) The expenses payable under paragraph (1) of this subsection are the expenses of round-trip travel of an employee, and the transportation of his immediate family, but not household goods, from his post of duty in Alaska or Hawaii to the place of his actual residence at the time of appointment or transfer to the post of duty, incurred after he has satisfactorily completed an agreed period of service in Alaska or Hawaii and in returning to his actual place of residence to take leave before serving another tour of duty at the same or another post of duty in Alaska or Hawaii under a new written agreement made before departing from the post of duty. (3) The payment of expenses of any employee and the transportation of his family under paragraph (1) of this subsection is limited to the expenses of travel and transportation incurred for not more than two round trips commenced within 5 years after the date the employee first commences any period of consecutive tours of duty in Alaska or Hawaii. (d) This section does not apply to appropriations for the Foreign Service of the United States.