Neb. Rev. Stat. § 81-1175

In examining the vouchers, bills, and requests for payment or reimbursement as provided for in section 81-1174 , no such voucher, bill, or request for travel expenses shall be approved unless written authorization for the same has been given by the (1) director, deputy director, or other titular head of the several state administrative departments, (2) elective or appointive state officer, (3) chairperson of a state commission, council, committee, or board, or (4) titular head or proper disbursing officer of any other state expending agency, including the University of Nebraska, state colleges, and state institutions, before such traveling expenses are incurred, except that such prior authority need not be obtained by peace officers of the State of Nebraska.