California's richest residents are opening their checkbooks to kill a wealth tax before voters can weigh in, with Google co-founder Sergey Brin alone pouring $82 million into the opposition and a small circle of tech billionaires driving the total anti-tax haul past $118 million ahead of the Nov. 3 ballot.

The measure, a one-time tax of up to 5% on the net worth of California residents worth more than $1 billion, became eligible for the November ballot on June 17 after Secretary of State Shirley Weber announced its signature count had cleared the state's random-sample threshold.

A last-minute offer from sponsor SEIU-United Healthcare Workers West to drop the initiative in exchange for a legislative 2% version was rejected by California Gov. Gavin Newsom, a Democrat, and negotiations collapsed before the June 25 withdrawal deadline.

Under the initiative, 90% of revenue would flow to Medi-Cal and other healthcare programs, with 10% split between food assistance and public education. The tax would apply to anyone who was a California resident as of Jan. 1.

Brin, who moved to Nevada last year, has emerged as the single largest donor to Building a Better California, the committee he co-founded with former Google CEO Eric Schmidt to sponsor two counter-initiatives on the same November ballot.

Business Insider reports his most recent contribution, a $16 million check, was cut May 15, roughly a month before the qualification deadline.

Kleiner Perkins Executive Chair John Doerr has given $10 million, former Sequoia Capital partner Michael Moritz $7.5 million, and Stripe CEO Patrick Collison $7 million, according to Business Insider's review of state filings.

The opposition has fanned out across multiple committees.

Ripple executive chairman Chris Larsen and his company, Ripple Labs, each put $5 million into Golden State Promise, a separate PAC opposing the tax outright and running eight-figure ad campaigns tied to the gubernatorial race.

Palantir co-founder Peter Thiel donated $3 million in December to the California Business Roundtable's political arm, part of the coalition arrayed against the measure; Thiel has been spending more time in Argentina, according to The New York Times.

Angel investor Ron Conway told Jack Altman's "Untapped" podcast in March that opponents were trying to get Newsom to broker a deal to keep the measure off the ballot, an effort that ultimately failed.

Backers of the tax, led by SEIU-UHW, have raised roughly $31 million, less than a quarter of the opposition haul.

Union President Dave Regan has argued the state needs the revenue, projected by proponents at $100 billion over five years, to blunt federal Medicaid cuts enacted under President Donald Trump's One Big Beautiful Bill Act.

The nonpartisan Legislative Analyst's Office estimates the tax would generate tens of billions of dollars up front but reduce annual state income tax revenue by hundreds of millions of dollars or more as high earners relocate.

Litigation is considered virtually certain if the measure passes, with legal challenges expected on retroactivity, apportionment, and bill of attainder grounds.