The US Environmental Protection Agency plans to revoke the 2009 endangerment finding, a scientific determination that greenhouse gases threaten human health and welfare, Bloomberg reported. The repeal, expected as early as Wednesday, underpins key federal rules governing emissions from cars, trucks, and other sources.

EPA Administrator Lee Zeldin described the move to the Wall Street Journal as “the largest act of deregulation in the history of the United States,” according to Bloomberg. The agency said last month that it had submitted a proposal to the Office of Management and Budget, and that a final rule will be issued once interagency review is completed.

The repeal follows a series of measures by the Trump administration to unwind US climate protections, including the formal withdrawal from the Paris Agreement last month and exits from major United Nations climate bodies, such as the Intergovernmental Panel on Climate Change and the UN Framework Convention on Climate Change.

Environmental organisations, including the Natural Resources Defense Council, have pledged to challenge any attempt to rescind the endangerment finding in court. The White House did not immediately respond to requests for comment.

The decision has been anticipated since the EPA first proposed scrapping the endangerment finding in July, marking what analysts view as a key step in dismantling federal climate regulations.