5 U.S.C. § 5942a

(a) Notwithstanding section 5536 of this title , and under regulations prescribed by the President, an employee of an Executive agency (other than a Government corporation) who is assigned to a post of duty at Johnston Island, a possession of the United States in the Pacific Ocean, is entitled to receive a separate maintenance allowance if the head of the employing agency finds that— (1) it is necessary for the employee to maintain the employee’s spouse or dependents, or both, at a location other than Johnston Island— (A) by reason of dangerous or adverse living conditions at Johnston Island; or (B) for the convenience of the Federal Government; and (2) the allowance is needed to help the employee meet the additional expenses involved in maintaining the employee’s spouse or dependents, or both, at such other location rather than at the post. (b) The regulations prescribed by the President shall include provisions for determining the rate at which an allowance under this section shall be paid.