U.S. Environmental Protection Agency chief Gina McCarthy on Friday finalized a determination that the landmark fuel efficiency rules instituted by President Barack Obama should be locked in through 2025, a bid to maintain a key part of his administration's climate legacy.

Major U.S. and foreign automakers have appealed to President-elect Donald Trump, who has been critical of Obama's climate policies, to review the rules requiring them to nearly double fleet-wide fuel efficiency by 2025, saying they impose significant costs and are out of step with consumer preferences.

As part of a 2012 regulation, EPA had to decide by April 2018 whether to modify the 2022-2025 model year vehicle emission rules requiring average fleet-wide efficiency of more than 50 miles per gallon. In November, the agency moved up the timetable for proposing that automakers can meet the 2025 standards.

McCarthy said in a statement her determination, a legally binding decision to maintain the fuel efficiency rules, rests on an extensive technical record.

"At every step in the process, the analysis has shown that the greenhouse gas emissions standards for cars and light trucks remain affordable and effective through 2025, and will save American drivers billions of dollars at the pump while protecting our health and the environment," she said.

Gloria Bergquist, a spokeswoman for the Alliance of Automobile Manufacturers, a trade association representing General Motors Co (GM.N), Ford Motor Co (F.N), Toyota Motor Corp (TM.N), Volkswagen AG and others, criticized the decision.

"Our fundamental priority remains striking the right balance to continue fuel economy gains and carbon reduction without compromising consumer affordability and vital auto-sector jobs," she said.

Automakers hope to work with regulators and California, Bergquist said, "to see whether we can find a prudent compromise path forward that avoids an unnecessary and counterproductive regulatory collision."

Legal experts have said it will be more difficult for the Trump administration and Congress to undo the determination than to unwind other regulatory actions issued by the Obama administration during its final months in office.

The 2025 determination is not a new regulation, so the EPA, under Trump, would likely have to go through an extensive process before withdrawing the determination, and could face lawsuits from environmental groups if they took that step.