Pub. L. 108-7, div. K, tit. IV, sec. 402

Sec. 402. No funds appropriated by this Act may be expended—(1) pursuant to a certification of an officer or employee of the United States unless—(A) such certification is accompanied by, or is part of, a voucher or abstract which describes the payee or payees and the items or services for which such expenditure is being made; or(B) the expenditure of funds pursuant to such certification, and without such a voucher or abstract, is specifically authorized by law; and(2) unless such expenditure is subject to audit by the General Accounting Office or is specifically exempt by law from such audit.