Following the enactment of appropriations by Congress, appropriations are not immediately available to federal agencies. A preliminary step in making funds available for obligation by departments and agencies is for OMB to release the funds to agencies in a process known as “apportionment.”
The purpose of apportionment is for OMB to make funds available to agencies in a measured way, in order to avoid budget authority running out prior to the end of a fiscal year, in other words, to avoid deficiencies, and the resulting necessity to request supplemental funds.
OMB typically apportions budget authority to departments and agencies in one of two ways: (1) by time periods (usually quarterly); or (2) by programs, projects, or activities. After OMB apportions budget authority to an agency, the recipient agency then makes allotments to officials or subunits within the agency, allowing them to incur obligations on behalf of the government.
An apportionment is legally binding, and any action that would financially obligate the federal government in excess of an apportionment is a violation of the Antideficiency Act. The Antideficiency Act prohibits federal employees from obligating or disbursing amounts in excess of an appropriation, apportionment, or allotment.
Agencies may, however, request reapportionments from OMB when unforeseen events have occurred. In addition, Congress may provide agencies with authority to reallocate funds from one appropriations account to another (“transfers”); or from one purpose, to another, within an appropriations account (“reprogramming”).
Apportionment is not a means by which the President may withhold funds appropriated by Congress. A President’s failure to make appropriated funds available for their congressionally intended purpose is prohibited by the Impoundment Control Act of 1974. For example, on January 16, 2020, the Government Accountability Office (GAO) ruled that the Trump Administration in the summer of 2019 had violated the Impoundment Control Act by attempting to use the apportionment process to withhold funds appropriated to the Department of Defense for security assistance to Ukraine.
A President may defer funds to later in a fiscal year or may propose to Congress a rescission of funds, but the withholding or impoundment of funds is an illegal encroachment on Congress’ constitutional power of the purse.