The White House confirmed Thursday that President Donald Trump has rescinded a 2009 federal finding that classified greenhouse gases as a threat to public health. The decision, first issued by the Environmental Protection Agency during Barack Obama’s administration, has served as the legal foundation for regulating emissions from vehicles, power plants, oil and gas facilities, and other industries.

Speaking in the Oval Office, Trump called the move the largest deregulation effort in US history. Administration officials said overturning the finding could lower costs for automakers by about $2,400 per vehicle and reduce energy and transportation expenses nationwide.

The 2009 determination concluded that six greenhouse gases, including carbon dioxide and methane, endangered public health. With Congress divided at the time, the finding became central to federal climate policy for more than a decade.

Environmental groups said they intend to challenge the action in court. Former President Barack Obama wrote that removing the finding would weaken public health protections. Legal analysts say the change may also prompt new state-level lawsuits and create uncertainty for US automakers competing in international markets.