31 U.S.C. § 1301

(a) Appropriations shall be applied only to the objects for which the appropriations were made except as otherwise provided by law. (b) The reappropriation and diversion of the unexpended balance of an appropriation for a purpose other than that for which the appropriation originally was made shall be construed and accounted for as a new appropriation. The unexpended balance shall be reduced by the amount to be diverted. (c) An appropriation in a regular, annual appropriation law may be construed to be permanent or available continuously only if the appropriation— (1) is for rivers and harbors, lighthouses, public buildings, or the pay of the Navy and Marine Corps; or (2) expressly provides that it is available after the fiscal year covered by the law in which it appears. (d) A law may be construed to make an appropriation out of the Treasury or to authorize making a contract for the payment of money in excess of an appropriation only if the law specifically states that an appropriation is made or that such a contract may be made.