5 U.S.C. § 4111: Acceptance of contributions, awards, and other payments

(a) To the extent authorized by regulation of the President, contributions and awards incident to training in non-Government facilities, and payment of travel, subsistence, and other expenses incident to attendance at meetings, may be made to and accepted by an employee, without regard to section 209 of title 18, if the contributions, awards, and payments are made by an organization determined by the Secretary of the Treasury to be an organization described by section 501(c)(3) of title 26 which is exempt from taxation under section 501(a) of title 26. (b) When a contribution, award, or payment, in cash or in kind, is made to an employee for travel, subsistence, or other expenses under subsection (a) of this section, an appropriate reduction, under regulations of the President, shall be made from payment by the Government to the employee for travel, subsistence, or other expenses incident to training in a non-Government facility or to attendance at a meeting.