Google cofounder Sergey Brin has emerged as the biggest donor opposing California’s proposed billionaire wealth tax, contribution $102 million to a political group fighting the measure that could leave him facing tax bill of about $13 billion if approved by voters.
The development was reported by Fortune, citing state financial campaign records. As per the campaign fillings, Brin has donated a teal of $102 million to building a Better California, a political action committee campaigning against California’s proposed wealth tax while supporting pro-business, housing and infrastructure policies. The contribution makes him the single largest founder of the anti-tax effort.
Opposition groups have collectively raised more than $187 million, compared with roughly $32 million raised by supporters of the measure.
What is California's
Proposition 40 will be on the ballot in November. It would impose a one-time 5% tax on California’s 200 billionaires. Ninety percent of the revenue would go to the state’s health care program. The remaining 10% would go to education, food assistance and administration. With a net worth of nearly $260 billion, Brin could owe about $13 billion if it passes.
Billionaires and line up against it
Former Google CEO Eric Schmidt and PayPal cofounder Peter Thiel have also donated to groups opposing the measure. Brin has likened the proposal to the socialist society he left behind. “I fled socialism with my family in 1979,” he told The New York Times in April, adding that he does not want California to end up in the same place.Gov. Gavin Newsom has also come out against the tax. He argues it would erode the state’s tax base and cut revenue for social services.
In an interview with Bloomberg Businessweek earlier this year, he said it would reduce investment in education, teachers, librarians, childcare, firefighting and police.
Billionaires already moving
Some of the wealthy are shifting their holdings out of the state. Brin now lists Nevada as his residence, according to state records, and reportedly bought a $51 million home near Miami Beach in March. Larry Page, Google’s other cofounder, has moved several assets out of California.
His family office, Koop, was incorporated in Delaware in December 2025. Oceankind, the ocean science nonprofit founded by his wife, Lucy Southworth, was incorporated there around the same time.
Debate over economic impact
Supporters of Proposition 40 argue the tax could generate about $100 billion over five years for state programmes. Opponents counter that it could encourage wealthy residents and businesses to leave California.However, a report cited by Fortune noted that California billionaires collectively paid about $4.1 billion in state income taxes last year, roughly 0.2% of their combined $2 trillion net worth. Researchers argued that even if every billionaire left the state, it would take decades for the loss of income tax revenue to offset the projected revenue generated by the proposed wealth tax.