43 U.S.C. § 1738

(a) The Secretary is authorized to enter into contracts for the use of aircraft, and for supplies and services, prior to the passage of an appropriation therefor, for airborne cadastral survey and resource protection operations of the Bureau. He may renew such contracts annually, not more than twice, without additional competition. Such contracts shall obligate funds for the fiscal years in which the costs are incurred. (b) Each such contract shall provide that the obligation of the United States for the ensuing fiscal years is contingent upon the passage of an applicable appropriation, and that no payment shall be made under the contract for the ensuing fiscal years until such appropriation becomes available for expenditure.