California’s governor, Gavin Newsom, called for a national “billionaires tax” on Friday as he fights a ballot measure targeting the ultra-wealthy in his home state.

Newsom, who is expected to run for president in 2028, published his proposal the day after California officials certified a ballot proposal to levy a one-time 5% tax on residents worth more than $1bn. The proposal, called the California Billionaire Tax Act, was brought by the Service Employees International Union-United Healthcare Workers West (SEIU-UHW) and would fund the state’s healthcare, education and food assistance programs.

The proposal has received more than 1.55m signatures, but has spurred intense pushback from the state’s richest residents as well as several other prominent labor unions.

“The dangerous wealth tax directly threatens vital funding for education and schools, healthcare and clinics, public safety, and infrastructure projects by making California’s revenue even more volatile,” a coalition of unions including the California Medical Association, California Primary Care Association and the California School Boards Association said in a joint statement on Friday.

Newsom strongly opposes the measure, arguing it will hurt the state’s economy.

In his Substack post on Friday, Newsom expanded on his opposition and framed it as an ineffective solution. “I understand the anxiety driving the wealth tax proposal in California. But I’m voting no because this measure dedicates almost all of the revenue it raises to a single category of state spending,” Newsom wrote.

Newsom argued that a state-level billionaire tax would be easily dodged by wealthy people who are able to move their assets to other states. Already, several billionaires, including Google co-founder Larry Page, have either threatened to leave California or made efforts to cut ties with the state.

“You may not be able to pick up and move to Texas or Florida to shelter your income from taxation, but I promise you that billionaires can, and do,” Newsom wrote. “Wealth is movable, and it shops for the state with the lowest taxes. The fight belongs at the federal level, where this broken system was created in the first place.”

In his Friday announcement, Newsom offered a counterproposal, a new national tax policy, rather than a state-by-state system. He proposed a minimum tax on anyone with a net worth above $100m. He also wants to make it illegal for the wealthy to borrow against their stock portfolios to fund their luxury lifestyles tax-free.

He also said the US government should own a stake in artificial intelligence companies, a policy that the senator Bernie Sanders has also advocated for in recent months.

Newsom said there should be new rules for inheritance taxes, warning that “the transfer of wealth among the ultra-wealthy will lock in a permanent American aristocracy of inherited wealth”. And he wants to raise corporate tax rates to where they were before Donald Trump’s first-term tax cut.

The need is especially urgent as artificial intelligence threatens to displace workers and further concentrate wealth, he wrote.

“We need to ensure every American owns a stake in the future being built by AI through a national public equity fund that takes a major stake in the new economy,” he wrote. “Simply, as artificial intelligence reshapes the country, every American should own a piece of the future it builds.”

Revenue generated by his proposals could be used to retrain workers, fund universal childcare, make college free and increase funding for healthcare.

Newsom’s proposals echo longstanding talking points of the Democratic party’s populist left, and he argued that urgent changes are needed to prevent the elite concentration of wealth and power from undermining democracy.

“It’s time for an economic reset for America,” Newsom wrote.

Newsom, who has drawn attention as one of Trump’s most high-profile political antagonists, is getting an early start on laying out a policy framework for his potential White House bid months before the midterm elections, which have typically marked the informal start of overt presidential campaigning.

The embrace of a wealth tax by Newsom, a moderate on tax policy despite his liberal reputation, signals a notable shift in the political landscape since the Massachusetts senator Elizabeth Warren struggled to get traction in her 2020 campaign, which she largely centered around a 2% wealth tax.

Newsom portrayed the nation’s tax code as a corrupt system built to help an elite few.

“Money buys influence, and influence rewrites the rules,” he wrote. “Those rewritten rules funnel even more wealth to the few. Under this weight, democracy itself starts to buckle.”

The Associated Press contributed reporting