Prop 40 opponents raise more than $300 million against California billionaire tax, roughly 10 times the Yes side

California voters will decide on Nov. 3 whether to impose the first tax on billionaire net worth in the United States. The campaign against it is among the most expensive ballot fights in state history.

Proposition 40 would levy a one-time 5% tax on people whose net worth topped $1 billion at the start of 2026. CalMatters puts the number of affected Californians at about 200. The Legislative Analyst's Office says a few hundred billionaires live in the state.

SEIU-United Healthcare Workers West, the union that put the measure on the ballot, projects it would raise roughly $100 billion over five years. Most of that money would go to health care, with the rest earmarked for food assistance and education.

The money

Opponents have raised more than $300 million, according to the Associated Press. State disclosures cited by The Guardian put the total above $340 million.

Google co-founder Sergey Brin has given at least $102 million, according to campaign finance filings. Former Google CEO Eric Schmidt is the second-largest donor. Others on the list include Palantir co-founder Peter Thiel, Stripe CEO Patrick Collison, DoorDash CEO Tony Xu and Ripple co-founder Chris Larsen.

The Yes side has raised about a tenth as much. The ad tracker AdImpact counts roughly $96 million in airtime and digital messaging spent or booked by opponents, against $209,000 from supporters.

The No campaign spent at least $21.2 million in the first 19 days of September, according to the latest filings. That is more than $1 million a day.

For Brin, the math is simple. Bloomberg's index estimates his net worth near $270 billion. CNN calculates that the tax would cost him nearly $14 billion.

Democrats on both sides

This is not a simple left-versus-right fight. Gov. Gavin Newsom, a Democrat, says he will vote no and is pushing a national billionaire tax instead. Both candidates to succeed him, Democrat Xavier Becerra and Republican Steve Hilton, also oppose Prop 40.

The California Teachers Association and Planned Parenthood Affiliates of California are in the No camp too, along with most Republicans. Their stated concern is that wealthy residents and their tax payments will leave the state. The top 1% of earners generate nearly half of California's personal income tax revenue.

"We're not opposed to the concept of a wealth tax," said Jodi Hicks, CEO of Planned Parenthood's California chapter. She said the group considers this proposal seriously flawed.

Health groups opposing the measure say they were not consulted in its design. They also say it does not solve the long-term problem of funding health care, since the tax is a one-time levy.

The Yes side includes major unions, Rep. Ro Khanna and Sen. Bernie Sanders. Sanders has held three California rallies. "Are we destined to live in an oligarchic society begging for crumbs while our economic and political lives are controlled by a handful of the wealthiest people on Earth?" he asked at one of them.

Supporters say the people who would pay benefited most from recent federal tax changes. They point to Congress cutting tens of billions of dollars from Medicaid, known as Medi-Cal in California. SEIU-UHW argues those cuts will close hospitals and clinics and cost thousands of jobs.

Polling and a built-in escape hatch

The Public Policy Institute of California's September poll found 52% of likely voters in favor and 46% opposed. Mail ballots are going out now, and the opposition is concentrating its spending in this stretch.

Prop 40 has a trapdoor. If Proposition 41 or 42 earns more votes than Prop 40, Prop 40 is nullified. Those competing measures would limit new special taxes, and CalMatters reports that Prop 40's opponents backed them. A Crypto Briefing report says Larsen has contributed to efforts supporting measures that could nullify the tax.

Legal questions

A Daily Wire opinion column argues the tax would face constitutional challenges even if voters approve it. The column says it applies retroactively to anyone living in California on Jan. 1, though the vote comes in November. It cites the Supreme Court's 1998 ruling in Eastern Enterprises v. Apfel, which called a different after-the-fact obligation "a severe, disproportionate, and extremely retroactive burden."

The column also argues that taxing a person's entire worldwide wealth based on a one-day residency snapshot violates due process and the commerce clause. No court has ruled on those claims, and the column is opinion, not a filing.

The Jan. 1 residency date is part of the measure's design. The point is to keep billionaires from leaving before the vote. The Daily Wire column says some prominent figures, including Larry Page, Thiel and Steven Spielberg, have left California anyway. The sources do not confirm where any of them now lives.

What happens next

CNN notes that the outcome could shape Newsom's expected 2028 presidential bid and the next governor's budget. Other states could treat the result as a model or as an invitation to recruit departing wealthy residents.

Voters have until Nov. 3. If Prop 40 passes without being nullified, its backers face the legal fight the column describes. Opponents' claim that the tax will drive revenue away would then be tested with real money.