5 U.S.C. § 5706c

section 5707 of this title Under regulations prescribed pursuant to , the head of an agency or department, or his or her designee, may use appropriations or other funds available to the agency for administrative expenses, for the reimbursement of Federal, State, and local income taxes incurred by an employee of the agency or by an employee and such employee’s spouse (if filing jointly), for any travel or transportation reimbursement made to an employee for which reimbursement or an allowance is provided.

Public Law 102–486 Reimbursements under this section shall include an amount equal to all income taxes for which the employee and spouse, as the case may be, would be liable due to the reimbursement for the taxes referred to in subsection (a). In addition, reimbursements under this section shall include penalties and interest, for the tax years 1993 and 1994 only, as a result of agencies failing to withhold the appropriate amounts for tax liabilities of employees affected by the change in the deductibility of travel expenses made by .