Subject to limitations in annual appropriation acts but notwithstanding any other law, a contract to which this chapter applies may, if authorized by the Secretary, be for any term of years not exceeding 5, if the contract provides for periodic adjustment of wages and fringe benefits pursuant to future determinations, issued in the manner prescribed in
section 6703 of this title at least once every 2 years during the term of the contract, covering each class of service employee.