Opponents Spend $300 Million to Block California Billionaire Tax

A spending gap of more than $268 million defines the final week of the campaign for California’s one-time 5 percent billionaire tax. David McCuan, a political science professor at Sonoma State University, identified the effort to defeat Proposition 40 as the most expensive ballot measure fight in state history. The vote is scheduled for November 3.

Donors opposing the measure include Google co-founder Sergey Brin, DoorDash founder Tony Xu, Stripe co-founder Patrick Collison, Ripple co-executive chairman Chris Larsen, and venture capitalists John Doerr, Michael Moritz, and Vinod Khosla. Together, they have contributed over $300 million. The pro-tax side has raised $32 million.

Mark Zuckerberg did not donate directly to the opposition, but his actions influenced the campaign. Meta’s SEC filings indicate he told the board, which includes Xu and Collison, that he would purchase a home outside the state to avoid the tax. The board subsequently created a new class of shares for him to use if the tax passed, a move that could have affected the company’s stock price.

The volume of advertising and mailers has caused confusion among voters. Brian Galle, a University of California at Berkeley economics professor who helped draft the proposal, said a flyer he received claimed the tax could apply to retirement savings, a detail not present in his original text. Ashley Craig, a volunteer with Patriotic Millionaires, reported hearing that the measure contains secret provisions. Any future changes to the tax would require a two-thirds majority in the state assembly.

Galle described the spending as evidence of the wealth disparity the tax aims to address. He noted the irony that billionaires are using their capital to prevent the measure from equalizing democratic influence, a dynamic he linked to the Supreme Court’s Citizens United v FEC ruling. Francesco Trebbi, a professor at Berkeley’s Haas School of Business, characterized the contest as a battle between Brin and millions of Californians that erodes public trust.

The measure has also exposed divisions within the Democratic Party. The state party endorsed the tax, but Craig said ground support from the organization has been limited. McCuan viewed the vote as a test between progressives and moderates, suggesting a win could inspire similar initiatives in the 2028 presidential race. Governor Gavin Newsom, who is considering a 2028 bid, opposes the tax as poorly written and warns it could drive away billionaires whose wealth the authors estimate at 2.3 trillion dollars. Gubernatorial candidate Xavier Becerra and former congresswoman Katie Porter also oppose the measure.

Opponents support two additional ballot measures: one banning new taxes on personal property or retroactive taxes, and the other requiring state auditors to review tax measures 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 blocking measures. Mark Baldassare, the institute’s survey director, noted that only about a third of citizen initiatives pass, placing the burden of proof on the yes side. Suzane Jiminez, chief of staff at the SEIU health workers union, reported that 3,000 volunteers are currently knocking on doors and that Senator Bernie Sanders and Congressman Ro Khanna have rallied support across the state.