California’s richest residents are digging deeper into their pockets to stop a ballot measure that would take a slice of their fortunes. Over the past few weeks, a handful of billionaires and wealthy tech figures have pumped tens of millions of additional dollars into fighting the California billionaire tax, a proposal that would impose a one-time 5% levy on anyone in the state holding more than $1 billion in assets. With the November election approaching, the fight over Proposition 40 has turned into one of the most expensive political battles in the state’s recent history.
Summary
Key takeaways
- Proposition 40 would levy a one-time 5% wealth tax on California residents worth more than $1 billion, with proceeds earmarked for healthcare funding.
- The opposition group Building a Better California has amassed $110 million as of late June and reserved $87 million in advertising ahead of November.
- A UC Berkeley poll found 48% of likely voters support the tax while 41% oppose it, with the split running largely along party lines.
- Google cofounder Sergey Brin has committed $102 million to fighting the measure, while entrepreneur Mark Cuban has warned publicly against it.
- Sens. Bernie Sanders and Ro Khanna have introduced federal legislation to extend a similar wealth tax nationwide.
Proposition 40’s One-Time Billionaire Wealth Tax
Proposition 40 targets a very specific group: Californians with net worths above $1 billion. If voters approve it, those residents would owe a single 5% tax on their assets, with the money directed toward boosting healthcare funding across the state. It’s not a recurring annual tax — the measure is designed as a one-time collection tied to the current wave of extreme wealth concentrated in California, home to some of the world’s richest tech founders and investors.
Scope and Purpose of the Tax
The measure’s backers frame it as a way to funnel new money into the state’s healthcare system by asking the wealthiest residents to contribute once, rather than through ongoing tax hikes. Because the threshold sits at $1 billion in assets, the tax would apply only to a small but extraordinarily wealthy slice of the population — the kind of individuals who built fortunes in venture capital, cryptocurrency, and Silicon Valley technology firms.
Voter Support and Political Split
Public opinion on the Proposition 40 wealth tax is close but leaning in favor of passage, at least for now. A survey conducted by UC Berkeley’s Institute of Governmental Studies, which polled more than 4,000 registered voters, found that 48% of likely voters back the measure while 41% oppose it. The breakdown reveals a familiar partisan pattern: registered Democrats overwhelmingly support the tax, only half of unaffiliated voters do, and roughly 80% of Republicans reject it outright.
Eric Schickler, co-director of the Institute of Governmental Studies, said the numbers point to a genuinely competitive race. “These results suggest that the Billionaires Tax initiative is shaping up to be a closely fought contest, with the key question being whether opponents can make big enough inroads among the state’s traditionally Democratic-leaning voters,” Schickler said in a press release.
The political lines don’t fall neatly, either. Gov. Gavin Newsom and Democratic gubernatorial candidate Xavier Becerra have both come out against the billionaire tax, even as the California Democratic Party formally endorsed it earlier this month — a split that shows the measure cuts across the usual party alignment inside California’s own Democratic establishment.
Opposition Backed by Building a Better California PAC
Standing at the center of the resistance is Building a Better California, a political action committee formed earlier this year specifically to defeat Proposition 40. The group’s financial muscle has grown rapidly, and its latest disclosures show just how seriously California’s wealthiest residents are treating the threat.
Major Donors and Funding
According to a campaign finance filing dated August 14 and reported by the Financial Times, venture capitalist John Doerr contributed $7.5 million to the PAC, while Ripple executive chair Chris Larsen added another $10 million. Smaller but still substantial sums came from Lookout co-founder John Hering, who gave $946,000, and Greenoaks Capital founder Neil Mehta, who contributed $250,000.
Those fresh contributions build on an already massive war chest. Building a Better California reported an endowment of $110 million as of late June, a total that has continued climbing as November draws closer. The scale of that fundraising signals just how much is at stake for California’s billionaire class if the measure passes.
Advertising Campaign and Counter-Propositions
Part of that money is going straight into persuasion. The PAC has reserved $87 million worth of advertising time ahead of the November election, according to reporting from the New York Times, an enormous sum aimed at shaping public opinion before voters head to the polls.
But advertising isn’t the group’s only strategy. Building a Better California has also backed two separate ballot measures, Proposition 41 and Proposition 42, that could neutralize the billionaire tax even if it wins. Before any special tax proposal could move forward, Proposition 41 would mandate that the state auditor conduct a review of reaches voters, while Proposition 42 would ban new taxes based purely on asset ownership, such as property that hasn’t been sold. If either counter-measure receives more votes than the billionaire tax, it would cancel it out — regardless of how Proposition 40 itself fares at the ballot box.
That detail matters more than it might seem. Awareness of these counter-propositions remains low: while 72% of voters surveyed had heard of the billionaire tax itself, fewer than a third knew that Propositions 41 and 42 even existed. That gap in voter awareness could end up deciding the outcome just as much as sentiment toward the tax itself.
Public and Political Reactions
Opposition to the California billionaire tax isn’t limited to campaign filings — it’s playing out publicly, too, with some of the state’s most recognizable wealthy figures speaking out directly.
Perspectives of Influential Billionaires
Google cofounder Sergey Brin has emerged as one of the tax’s most determined opponents. Brin, who moved a significant portion of his assets out of California late last year, has now put $102 million toward fighting the measure, after adding a fresh $20 million contribution to Building a Better California earlier this month.
Mark Cuban has also weighed in, warning that the tax could push entrepreneurs out of the state entirely. In an exchange on X with California Congressman Ro Khanna, Cuban didn’t hold back: “IMO, if this passes, only idiot startup founders stay in Cali,” he wrote, framing the measure as a direct threat to the state’s startup ecosystem.
Political and Legislative Responses at State and National Levels
On the other side of the debate, Sen. Bernie Sanders has championed the idea that billionaires should shoulder more of the tax burden. Sanders said in February that the measure would show the wealthiest Americans “we are still living in a democratic society where the people have some power.”
Sanders didn’t stop at California. Alongside Rep. Ro Khanna, he introduced federal legislation in March known as the “Make Billionaires Pay Their Fair Share Act.” The Bernie Sanders wealth tax proposal would apply a 5% levy on America’s 938 billionaires, with proceeds meant to expand Medicare, reverse Medicaid cuts tied to President Trump’s Big Beautiful Bill, and send a $3,000 direct payment to every person in households earning $150,000 or less.
That federal push underscores why California’s fight matters well beyond state lines. If Proposition 40 passes and survives its own counter-measures, it could become a working model — or a cautionary tale — for lawmakers pushing similar wealth taxes at the national level.
FAQ
What does Proposition 40 propose regarding wealth tax?
Proposition 40 proposes a one-time 5% wealth tax on California residents with assets over $1 billion to increase healthcare funding in the state.
Who are the major opponents of Proposition 40 and what resources have they mobilized?
The Building a Better California PAC, backed by billionaires like John Doerr and Chris Larsen, opposes the tax and has raised $110 million, reserving $87 million for advertising ahead of the November election.
How is public opinion divided on Proposition 40?
A UC Berkeley poll shows 48% of likely California voters support the tax while 41% oppose it, with support and opposition split significantly along party lines.
Are there any counter-propositions related to the billionaire tax?
Yes. Propositions 41 and 42, backed by the same PAC, would cancel out the billionaire tax if either receives more votes, even if Proposition 40 itself passes.
Article produced with the assistance of artificial intelligence and reviewed by the editorial team.
