5 U.S.C. § 5942

(a) Notwithstanding section 5536 of this title , an employee of an Executive department or an independent establishment who is assigned to duty, except temporary duty, at a site so remote from the nearest established communities or suitable places of residence as to require an appreciable degree of expense, hardship, and inconvenience, beyond that normally encountered in metropolitan commuting, on the part of the employee in commuting to and from his residence and such worksite, is entitled, in addition to pay otherwise due him, to an allowance of not to exceed $10 a day. The allowance shall be paid under regulations prescribed by the President establishing the rates at which the allowance will be paid and defining and designating those sites, areas, and groups of positions to which the rates apply. (b) Under procedures prescribed by the President, the maximum allowance specified in subsection (a) may be adjusted from time to time in the interest of recruiting and retaining employees for performance of duty at remote worksites.