31 U.S.C. § 1107: Deficiency and supplemental appropriations

The President may submit to Congress proposed deficiency and supplemental appropriations the President decides are necessary because of laws enacted after the submission of the budget or that are in the public interest. The President shall include the reasons for the submission of the proposed appropriations and the reasons the proposed appropriations were not included in the budget. When the total proposed appropriations would have required the President to make a recommendation under section 1105(c) of this title if they had been included in the budget, the President shall make a recommendation under that section. The President shall transmit promptly to Congress without change, proposed deficiency and supplemental appropriations submitted to the President by the legislative branch and the judicial branch.