California's gasoline efficiency rules apply to about 40 percent of the cars sold in this country.
But they ultimately might not, if this state and a dozen others, lose a fight with Uncle Sam.
U.S. automakers have accused the Obama Administration of fast-tracking California's fuel-efficiency rules before Donald Trump became president, well ahead of next year's deadline.
Now the influential anti-pollution standards are right in the crosshairs of an Environmental Protection Agency process that’s expected to prompt a rollback.
New cars hitting the pavement in California keep getting better mileage than counterparts sold in most of the country.
By 2025, the state's latest standards, finalized in January, will require them to average about 54 miles per gallon.
"We're thriving here in California; we're one of the largest economies in the world,” says Nicole Capretz, founder of the Climate Action Campaign in San Diego. “And we have the most clean energy and clean car standards."
But automakers take issue with California's authority to impose rules stronger than Uncle Sam's -- rules that a dozen other states have followed.
Now, after the stricter mileage standards for 2022-2025 cars and light duty trucks undergo an executive-ordered review by the Environmental Protection Agency, climate change activists fear they’ll be greatly reduced.
California has gotten dozens of waivers from the feds, but the EPA is now calling those into question.
"And we're ready for the fight,” said Nicola Peill-Moelter, an activist with the SanDiego350.org. “We think the current standards are very good for the country, good for the economy, good for innovation, and obviously good for the climate."
While the manufacturers say environmental regulations can be unreasonable burdens, they've managed to develop leading-edge technologies that have benefitted the industry -- along with buyers.
"The consumer will save three times over the lifetime of the vehicle than they'll pay in the initial cost of the industry,” Peill-Moelter told NBC 7 in an interview Wednesday. “So it's a win-win."
Meantime, a news release issued by Gov. Brown’s office called the President's executive order "a cynical ploy" that amounts to an "unconscionable gift to polluters".
The state also announced it’s taking on a leading auto industry group in a lawsuit, now on appeal in a U.S. Circuit Court, that's challenging the California's standards.