10 USC 1591 – Reimbursement for travel and transportation expenses when accompanying Members of Congress
(a) Subject to subsection (b), the Secretary concerned may authorize reimbursement to a civilian employee who is accompanying a Member of Congress or a congressional employee on official travel for actual travel and transportation expenses incurred for such travel.
(b) The allowance provided in subsection (a) may be paid—
(1) at a rate that does not exceed the rate approved for official congressional travel; and
(2) only when the travel of the member is directed or approved by the Secretary concerned.
(c) In this section:
(1) The term “Member of Congress” means a member of the Senate or the House of Representatives, a Delegate to the House of Representatives, and the Resident Commissioner from Puerto Rico.
(2) The term “congressional employee” means an employee of a Member of Congress or an employee of Congress.
(3) The term “Secretary concerned” includes the Secretary of Defense with respect to civilian employees of the Department of Defense other than a military department.