Trump was joined in the Oval Office by the CEOs of Ford and Stellantis, as well as a General Motors official to announce the move, signaling buy-in from the "Big Three" automakers.

"My administration is taking historic action to lower costs for American consumers, protect American auto jobs and make buying a car much more affordable," the president said.

"Today is a victory (for) common sense and affordability," Ford CEO Jim Farley chipped in.

Environmentalists quickly pushed back, saying the move stood out even among Trump's many anti-green actions because of its outsized impact on car-dependent America.

"Trump is taking a wrecking ball to the biggest single step any nation has ever taken to combat oil use, global warming pollution, and helping save consumers money at the gas pump," Dan Becker, an activist with the Center for Biological Diversity, told AFP. "This is the big one."

At stake are the Corporate Average Fuel Economy (CAFE) standards, created in 1975 in response to the Arab oil embargo, which require vehicles to achieve the "maximum feasible" mileage per gallon.

The full extent of the rollback was not immediately clear.

But the Trump administration has repeatedly signaled opposition to efficiency increases enacted under Joe Biden's administration, which boosted targets by 8-10 percent, aiming for more than 50 miles per gallon by 2031.

Trump's Department of Transport has argued that Biden officials improperly factored in electric and hybrid vehicles, saying the standards would be unattainable for gasoline-powered cars and would effectively force a shift in the market.

Becker called that argument "ludicrous" because it would force automakers to ignore that advanced technology exists.

- Trump EV fight -

Trump has railed against what he calls an EV "mandate" -- an issue that has put him at odds with his on-again, off-again billionaire ally Elon Musk, the CEO of Tesla, which still has the highest EV market share in the United States.

Republicans in Congress have repealed clean-energy tax credits in a major tax and spending bill, and targeted California's ability to set its own vehicle-emission limits.

Throughout 2025, GM and other US automakers have curtailed or pushed back new EV plant capacity.

But whether savings from reduced EV investment will filter through to consumers remains unclear.

While the shift away from EVs does allow automakers to delay or forgo billions of dollars in new investments, some funds are being steered into new initiatives to add US carbuilding capacity in light of Trump's tariffs.

"Meeting high fuel economy standards has been challenging for the auto industry and has added to vehicle cost," Charlie Chesbrough, an analyst with Cox Automotive, told AFP.

"However, consumers like fuel efficient vehicles. This year traditional hybrids are up double digits from last year while gas vehicles are basically flat," he added.

"Since most consumers don't have transportation alternatives available, people fear high gas prices. And good MPG is a way to mitigate that risk."

Gina McCarthy, a former senior official under Biden and Barack Obama, said the move would harm the auto industry by slowing its shift to electric vehicles and worsen climate change.

"The rest of the world will continue to innovate and create cleaner cars that people want to buy and drive, while we're forced to sit in our clunkers, paying more for gas, and pumping out more tailpipe emissions."