5 U.S.C. § 5538

(a) An employee who is absent from a position of employment with the Federal Government in order to perform active duty in the uniformed services pursuant to a call or order to active duty under section 12304b of title 10 or a provision of law referred to in section 101(a)(13)(B) of title 10 shall be entitled, while serving on active duty, to receive, for each pay period described in subsection (b), an amount equal to the amount by which— (1) the amount of basic pay which would otherwise have been payable to such employee for such pay period if such employee’s civilian employment with the Government had not been interrupted by that service, exceeds (if at all) (2) the amount of pay and allowances which (as determined under subsection (d))— (A) is payable to such employee for that service; and (B) is allocable to such pay period. (b) Amounts under this section shall be payable with respect to each pay period (which would otherwise apply if the employee’s civilian employment had not been interrupted)— (1) during which such employee is entitled to re-employment rights under chapter 43 of title 38 with respect to the position from which such employee is absent (as referred to in subsection (a)); and (2) for which such employee does not otherwise receive basic pay (including by taking any annual, military, or other paid leave) to which such employee is entitled by virtue of such employee’s civilian employment with the Government. (c) Any amount payable under this section to an employee shall be paid— (1) by such employee’s employing agency; (2) from the appropriation or fund which would be used to pay the employee if such employee were in a pay status; and (3) to the extent practicable, at the same time and in the same manner as would basic pay if such employee’s civilian employment had not been interrupted. (d) The Office of Personnel Management shall, in consultation with Secretary of Defense, prescribe any regulations necessary to carry out the preceding provisions of this section. (e) (1) The head of each agency referred to in section 2302(a)(2)(C)(ii) shall, in consultation with the Office, prescribe procedures to ensure that the rights under this section apply to the employees of such agency. (2) The Administrator of the Federal Aviation Administration shall, in consultation with the Office, prescribe procedures to ensure that the rights under this section apply to the employees of that agency. (f) For purposes of this section— (1) the terms “employee”, “Federal Government”, and “uniformed services” have the same respective meanings as given those terms in section 4303 of title 38 ; (2) the term “employing agency”, as used with respect to an employee entitled to any payments under this section, means the agency or other entity of the Government (including an agency referred to in section 2302(a)(2)(C)(ii)) with respect to which such employee has reemployment rights under chapter 43 of title 38; and (3) the term “basic pay” includes any amount payable under section 5304.