The California Air Resources Board ( CARB) proposed maintaining strict Obama-era rules mandating rising fuel efficiency requirements annually through 2025. The Trump administration has proposed freezing federal vehicle emissions requirements at 2020 levels through 2026.
"California will take all actions to ensure that the smart standards we developed in partnership with the auto industry to cut greenhouse gas emissions from vehicles stay in place," said CARB Chair Mary Nichols in a statement from Sacramento.
"Dirty, gas guzzling vehicles are a direct assault on public health, and foreclose our ability to rein in air pollution and greenhouse gases," she added.
California's decision is nationally significant because the state is the largest U.S. auto market. Also, a dozen states and the District of Columbia have adopted California's emissions rules, accounting for more than a third of all U.S. vehicle sales.
California is seeking public comments on ways to make the rules more flexible while still meeting goals to reduce carbon emissions.
The Trump administration said the Obama era rules were "not appropriate" and its freeze would help make vehicles more affordable. It said that under its proposal vehicles would average 37 miles per gallon in 2026, compared with 46.8 mpg under the Obama rule.
California and 18 other states said last week they will fight the Trump administration's freeze in court, a legal battle that could leave automakers in regulatory limbo for years.
Last month, Nichols told Reuters California wants to work with automakers on revisions and she sees a "window" for a deal in coming months.
Two trade groups representing General Motors Co, Volkswagen AG, Toyota Motor Corp and other major automakers, sent letters to California Governor Jerry Brown and U.S. President Donald Trump last week urging negotiations for a compromise on one set of nationwide rules.
Automakers want changes to address shifts in consumer demand but also favor efficiency requirements continuing to rise.
California said under the Trump administration's preferred option, emissions could increase by almost 14 million metric tons per year by 2025. The administration says freezing the limits would have little impact on average global temperature, even as projected U.S. oil consumption would increase by about 500,000 barrels daily.
California has received a waiver to set its own emissions rules as well as authority to require automakers to build a rising number of zero-emission vehicles. The Trump administration has proposed revoking that authority.
Reporting by David Shepardson.