41 CFR § 301-11.602 - Tax consequences of extended TDY.
(a) For a taxable extended TDY assignment, all travel expense allowances, reimbursements, and direct Government payments made on the employee's behalf in connection with the assignment become taxable income, starting from the date the assignment is recognized as exceeding one year. The agency will reimburse the employee for substantially all income taxes incurred as a result of their taxable extended TDY assignment, through two components:
(1) Withholding Tax Allowance (WTA); and
(2) Extended TDY Tax Reimbursement Allowance (ETTRA).
(b) The WTA and ETTRA cover only TDY benefits described in this subchapter. On an extended TDY assignment, the employee is not eligible for relocation benefits they would have received on a permanent relocation.