31 U.S.C. § 1516

An official designated in section 1513 of this title to make apportionments may exempt from apportionment— (1) a trust fund or working fund if an expenditure from the fund has no significant effect on the financial operations of the United States Government; (2) a working capital fund or a revolving fund established for intragovernmental operations; (3) receipts from industrial and power operations available under law; and (4) appropriations made specifically for— (A) interest on, or retirement of, the public debt; (B) payment of claims, judgments, refunds, and drawbacks; (C) items the President decides are of a confidential nature; (D) payment under a law requiring payment of the total amount of the appropriation to a designated payee; and (E) grants to the States under the Social Security Act ( 42 U.S.C. 301 et seq.).