Yes, generally you must have written or electronic authorization before incurring any travel expense. When it is not practicable or possible to obtain such authorization before travel begins, your agency may approve reimbursement for specific travel expenses after travel is completed. However, written or electronic advance authorization is required for items in § 301-2.5(c), (i), (n), and (o) of this part.
41 C.F.R. §301-2.1