Brin and Tech Leaders Back $300 Million Push to Stop California Prop 40

Sergey Brin, Tony Xu, and other tech leaders have donated more than $300 million to defeat a proposed one-time tax on California billionaires. The group aims to block Proposition 40 before voters cast ballots on November 3. This spending makes the campaign the most expensive ballot measure fight in U.S. history, according to David McCuan, a political science professor at Sonoma State University.

The measure would impose a 5 percent tax on the assets of individuals worth more than $1 billion. Supporters have raised only $32 million for the campaign. The vast disparity in funding has created a significant imbalance in advertising and direct mail. McCuan tracks state and local elections and confirmed the record-breaking nature of the expenditure.

The opposition includes prominent figures from the tech industry. Alongside Brin, who co-founded Google, the donors include Tony Xu of DoorDash and Patrick Collison of Stripe. Other backers are Chris Larsen of Ripple and venture capitalists John Doerr, Michael Moritz, and Vinod Khosla. Mark Zuckerberg of Meta has not donated to the opposition, though his company’s filings revealed he plans to buy a home outside California to avoid the tax.

Confusion among voters has grown due to the volume of materials sent to homes. Brian Galle, an economics professor at the University of California at Berkeley and one of the proposal’s authors, said a flyer he received claimed the tax could apply to anyone, including retirement savings. He stated that these details were not in the original text. Ashley Craig, a volunteer with the pro-tax group Patriotic Millionaires, reports that voters often believe the measure has secret provisions that would tax everyone.

Galle argued that the spending demonstrates the inequality the tax aims to address. He noted that while Proposition 40 is meant to make democracy more equal, billionaires are using their money to avoid that outcome. Francesco Trebbi, a professor at Berkeley’s Haas School of Business, described the contest as a battle between Sergey Brin and millions of Californians. He said this dynamic erodes trust in the political system.

The fight has also exposed divisions among Democrats. The state party endorsed the tax, but Craig said she has received little ground support from the party. McCuan described the measure as a proxy test between progressives and moderates. A success could encourage progressive candidates to try similar ideas in the 2028 presidential race. Governor Gavin Newsom opposes the tax, calling it poorly written and warning it would harm the state if billionaires leave.

Opponents have also backed two other ballot measures. One bars new state taxes on personal property or those imposed retroactively. The other requires state auditors to review proposed tax measures for financial impact before a vote. If either passes with more votes than the billionaire tax, it could negate the tax even if voters approve it. A recent Public Policy Institute of California poll found voters narrowly support the tax but also back the two measures aimed at stopping it.

Suzane Jiminez, chief of staff at the SEIU health workers union which sponsored the measure, said she feels confident about the outcome. She reported that 3,000 volunteers have recently been knocking on doors and distributing flyers. Senator Bernie Sanders and Congressman Ro Khanna have also rallied support across the state. McCuan suggested that even a defeat could benefit backers, who could blame moderates and target big tech as a political bogeyman.