5 U.S.C. § 5702: Per diem; employees traveling on official business

a per diem allowance at a rate not to exceed that established by the Administrator of General Services for travel within the continental United States, and by the President or his designee for travel outside the continental United States; reimbursement for the actual and necessary expenses of official travel not to exceed an amount established by the Administrator for travel within the continental United States or an amount established by the President or his designee for travel outside the continental United States; or a combination of payments described in subparagraphs (A) and (B) of this paragraph. Any per diem allowance or maximum amount of reimbursement shall be established, to the extent feasible, by locality. The Secretary of Defense shall not alter the amount of the per diem allowance, or the maximum amount of reimbursement, for a locality based on the duration of the travel in the locality of an employee of the Department. For travel consuming less than a full day, the payment prescribed by regulation shall be allocated in such manner as the Administrator may prescribe. because of an incapacitating illness or injury which is not due to the employee’s own misconduct is entitled to reimbursement for expenses of transportation to the employee’s designated post of duty, or home or regular place of business, as the case may be, and to payments pursuant to subsection (a) of this section until that location is reached; or because of a personal emergency situation (such as serious illness, injury, or death of a member of the employee’s family, or an emergency situation such as fire, flood, or act of God), may be allowed, with the approval of an appropriate official of the agency concerned, reimbursement for expenses of transportation to the employee’s designated post of duty, or home or regular place of business, as the case may be, and payments pursuant to subsection (a) of this section until that location is reached. reimbursement for expenses of transportation to the location where necessary medical services are provided or the emergency situation exists, payments pursuant to subsection (a) of this section until that location is reached, and such reimbursement and payments for return to such assignment. The reimbursement which an employee may be allowed pursuant to subparagraph (A) of this paragraph shall be the employee’s actual costs of transportation to the location where necessary medical services are provided or the emergency exists, and return to assignment from such location, less the costs of transportation which the employee would have incurred had such travel begun and ended at the employee’s designated post of duty, or home or regular place of business, as the case may be. The payments which an employee may be allowed pursuant to subparagraph (A) of this paragraph shall be based on the additional time (if any) which was required for the employee’s transportation as a consequence of the transportation’s having begun and ended at a location on the travel assignment (rather than at the employee’s designated post of duty, or home or regular place of business, as the case may be). Subject to the limitations contained in regulations prescribed pursuant to section 5707 of this title , an employee who is described in subsection (a) of this section and who interrupts the travel assignment prior to its completion because of an incapacitating illness or injury which is not due to the employee’s own misconduct is entitled to payments pursuant to subsection (a) of this section at the location where the interruption occurred. This section does not apply to a justice or judge, except to the extent provided by section 456 of title 28 . The term ‘agency’ has the meaning given that term under section 5701 of title 5 , United States Code. The term ‘general public’ includes the Federal Government or an agency. To the extent provided under subsection (c), a Federal employee, member of the Foreign Service, member of a uniformed service, any family member or dependent of such an employee or member, or other individual who receives a promotional item (including frequent flyer miles, upgrade, or access to carrier clubs or facilities) as a result of using travel or transportation services obtained at Federal Government expense or accepted under section 1353 of title 31 , United States Code, may retain the promotional item for personal use if the promotional item is obtained under the same terms as those offered to the general public and at no additional cost to the Federal Government. is at the expense of an agency; or is accepted by an agency under section 1353 of title 31 , United States Code; and does not apply to travel by any officer, employee, or other official of the Government who is not in or under any agency. Any agency with authority to prescribe regulations governing the acquisition, acceptance, use, or disposal of any travel or transportation services obtained at Government expense or accepted under section 1353 of title 31 , United States Code, may prescribe regulations to carry out subsection (b) with respect to those travel or transportation services. This section shall apply with respect to promotional items received before, on, or after the date of enactment of this Act [ Dec. 28, 2001 ].”