California voters are two weeks away from deciding whether the state's billionaires should hand over a one-time slice of their fortunes — and the fight over Proposition 40 has turned into one of the most expensive, closely-watched ballot brawls in the country.

Formally titled the California Billionaire Tax Act, Prop 40 would impose a one-time 5% tax on the net worth of any individual or married couple worth more than $1 billion as of December 31, 2026, according to the official Legislative Analyst's Office ballot analysis. Those on the hook could spread payment over five annual installments, and the measure is written to apply retroactively from January 1, 2026 — language designed specifically to stop billionaires from dodging the bill simply by relocating out of state once the policy takes effect.

A Polling Dead Heat

The measure, which goes before voters November 3, is sitting on a knife's edge. A UC Berkeley Institute of Governmental Studies survey in August found 48% of likely voters supporting it against 41% opposed, while a September poll from the Public Policy Institute of California put support higher, at 52% to 46% opposed. The California Democratic Party's executive board voted to formally endorse Prop 40, but the measure has split the party's own establishment: Gov. Gavin Newsom, former Attorney General Xavier Becerra and former Fox News commentator-turned-political strategist Steve Hilton have all come out against it, alongside the California Teachers Association and major business lobbies.

A ONE-TIME TAX, A PERMANENT FIGHT

Opponents haven't limited themselves to messaging. They've successfully qualified two competing measures, Propositions 41 and 42, which supporters say are designed to potentially neutralize Prop 40's effects even if it passes at the ballot box — setting up the possibility that California voters could approve a billionaire tax in November only to see its implementation challenged or undercut by a companion measure passed the same day.

Economists Warn of Exodus Risk

A Stanford economics analysis cited by CBS News MoneyWatch cautions that the tax could carry unintended consequences, warning that a one-time wealth levy on this scale risks accelerating the departure of ultra-wealthy residents and the businesses and investment capital that tend to follow them, even with the retroactive filing date meant to blunt that effect. Supporters counter that the money — which backers say could run into the billions of dollars depending on how many billionaires remain California residents on the qualifying date — is badly needed for public services at a time when the state has repeatedly faced multibillion-dollar budget gaps.

With early voting already underway in parts of the state, both campaigns are pouring money into the race's final stretch, and California's billionaire class — one of the largest concentrations of extreme wealth in the country — is watching the Nov. 3 results as closely as anyone.