A Google founder has more than doubled his financial contribution to the fight against a proposed wealth tax in California. New filings with the state show that former Alphabet president Sergey Brin donated $25m to a Super Pac dedicated to blocking the tax on top of $20m he had already given.

Brin is not alone among Google’s top brass in upping his financial stake in the campaign against the ballot proposal. The company’s former CEO Eric Schmidt donated $1.02m, adding to a previous $2m contribution.

The tech titans are battling the California Billionaire Tax act, often referred to simply as the billionaire tax. It’s a proposed ballot measure that would require any California resident worth more than $1bn to pay a one-off, 5% tax on their assets to help cover education, food assistance and healthcare programs in the state. It’s sponsored by the Service Employees International Union-United Healthcare Workers West, and is still in the signature-gathering phase.

If the measure reaches the ballot and gains voters’ approval, the tax would apply to billionaires based on their residency as of 1 January 2026. For Brin, worth about $247bn, the bill would likely be upwards of $12bn. That stipulation appears to have caused him and several other billionaires to leave California at the end of last year. Brin relocated to a $42m estate on the north-eastern shore of Lake Tahoe in Nevada, and his Pac donations show Reno as his address. Schmidt’s filings show his address as West Hollywood.