41 C.F.R. § 302-17.20 – Purpose of the WTA.

(a) The purpose of the WTA is to protect an employee from having to use part of their relocation expense reimbursements to pay Federal income tax withholding; it does not cover State taxes, local taxes, Medicare taxes, or Social Security taxes (see § 302-17.21(c) and (d)).
(b) The WTA may be optional to employees. Employees should review § 302-17.61 for discussion about choosing whether or not to accept the WTA. See §§ 302-17.62 through 302-17.67 for procedures if an employee chooses not to accept the WTA.