The president-elect has said repeatedly he would scrap what he called the "electric vehicle mandate" -- actually a $7,500 federal rebate for anyone who purchases an EV.
Gavin Newsom, who heads the solidly Democratic state and has pitched himself as a leader of the anti-Trump political resistance, said Monday California was not "turning back" towards polluting transport.
"We will intervene if the Trump Administration eliminates the federal tax credit, doubling down on our commitment to clean air and green jobs in California," Newsom said.
"We're not turning back on a clean transportation future -- we're going to make it more affordable for people to drive vehicles that don't pollute," he added.
"Consumers continue to prove the skeptics wrong -– zero-emission vehicles are here to stay."
If Trump scraps the tax credit, California could revive its own Clean Vehicle Rebate Project, which ran until November 2023, granting rebates of up to $7,500 for people buying battery-powered cars, a press release said.
California leads the nation in electric vehicle adoption, and is the single biggest market in the country, representing around a third of all units sold in the United States.
State figures show that more than two million so-called "zero emission vehicles" -- which include fully electric vehicles as well as plug-in hybrids -- have now been sold in the state, with one-in-four new cars in that category.
On the campaign trail, Trump was frequently hostile to electric vehicles, which he has linked with what he calls the "hoax" of climate change.
He vowed repeatedly that under his watch the United States would become "energy dominant," chiefly through expanded oil and gas extraction.
For many in California, such pledges are anathema, with the state frequently battered by the tangible effects of climate change, from huge wildfires to droughts to furious storms.
Newsom -- who many believe has White House ambitions of his own -- has positioned himself as a bulwark against the feared excesses of an incoming Trump administration on issues from climate change to immigration, vowing to be a check on its power.
With 40 million people, the sheer size of California's market has for a long time helped set the national tone when it comes to pollution standards for automakers.
Rather than make two versions of the same vehicles, Detroit giants have willingly adopted California's tougher rules on emissions and efficiency for nationwide sales.
That de facto standard-setting power has angered Republicans like Trump, who say -- on this issue -- states should not be allowed to set their own rules.
