WASHINGTON, DC (WOWO) The Environmental Protection Agency has rescinded a 2009 determination that greenhouse gases endanger public health and welfare, a move that had formed the legal basis for federal vehicle emissions standards.

According to reporting from Fox News, EPA Administrator Lee Zeldin announced the action Thursday, describing it as the largest deregulatory move in U.S. history. The 2009 endangerment finding concluded that carbon dioxide, methane, nitrous oxide and other greenhouse gases qualify as pollutants under the Clean Air Act, following the Supreme Court’s ruling in Massachusetts v. EPA.

The finding led to a series of federal emissions standards for vehicles and engines. A source familiar with the matter told Fox News that all federal greenhouse gas emissions standards for vehicles and engines stemming from the 2009 declaration will be rescinded.

Zeldin said the agency is prioritizing consumer choice and eliminating regulations he described as burdensome, including credits tied to auto start-stop technology adopted by some manufacturers to meet emissions standards.

Environmental advocacy organization Earthjustice signaled plans to challenge the decision in court. Colorado Governor Jared Polis said in a statement he supports maintaining science-based air quality standards.

The EPA action is expected to prompt legal review as implementation moves forward.