Yes, unless you have an exception to the use of the ETS (see § 301-50.4 of the chapter and §§ 301-73.102 and 301-73.104), agencies and employees must use the ETS for all temporary duty travel. The Department of Defense, the legislative branch, and the Government of the District of Columbia are not subject to this requirement.
41 C.F.R. §§301-73.100