Any amount advanced to an employee for allowable travel expenses but not used for such purposes is recoverable from the employee, in accordance with 5 U.S.C. 5705, by salary offset without regard to the due process provisions in §1506.22. This section does not apply to debts where collection by salary offset is explicitly prohibited by another statute. Collection of debt by salary offset will be in accordance with 5 U.S.C. 5514.