August 18, 2026 - By Edward Lempinen - Proposition 40, the controversial measure to impose a one-time tax on California billionaires, has the support of 48% of likely voters ahead of November’s election, with 41% opposed, according to a new report by the UC Berkeley IGS Poll.

The poll, released Friday Aug. 14, also found that likely voters are leaning against Proposition 39, which would establish strict ID requirements at the polls: 51% opposed to it and 42% in favor.

The polling shows partisan splits on both measures, with Democrats and liberals expressing strong support of the tax-the-rich measure and Republicans and conservatives registering strong support for the voter ID requirements.

“These results suggest that the billionaire tax initiative is shaping up to be a closely fought contest, with the key question being whether opponents can make big enough inroads among the state’s traditionally Democratic-leaning voters,” said political scientist Eric Schickler, co-director of the UC Berkeley Institute of Governmental Studies (IGS).  

“By contrast,” Schickler added, “foes of the Voter ID initiative have already started to solidify, making it a more typical Democratic-Republican fight, in which Democrats in California generally hold the advantage.”

Proposition 40 would apply to an estimated 200 California billionaires, requiring them to pay a one-time 5% tax. Supporters argue that the tax would apply to Californians who benefitted the most from the Republican-backed “One Big Beautiful Bill,” which reduced taxes for the wealthiest Americans while cutting medical support and other social spending for low-income people in California and nationwide.

Proposition 40 sponsors project that it would raise roughly $100 billion over five years, with funds channeled mostly to healthcare, but also to food assistance and education.

The measure is strongly opposed by many business groups in Silicon Valley and beyond. Billionaire Sergey Brin, the co-founder of Google, has spent more than $100 million on ads opposing Proposition 40. 

Brin and others also support two competing ballot measures — Proposition 41 and Proposition 42 — that would effectively void the billionaire tax. The IGS Poll found that voter awareness of those measures is low, and that voters who hear the official ballot summaries have divided opinions.

Proposition 40 has created some divisions among the state’s Democrats; Gov. Gavin Newsom and gubernatorial candidate Xavier Becerra are opposed, but the state party is officially in favor.

Overall, 70% of likely Democratic voters in the IGS Poll favored the billionaire tax measure, with support rising to 86% among voters who identify as strongly liberal. Among Republican likely voters, 80% opposed the measure. Voters with no party preference were split.

Younger voters by a wide margin were more likely to support Proposition 40, the poll found.

Berkeley IGS Poll Director Mark DiCamillo noted another striking number: 72% of voters have heard of the billionaire tax initiative, “an unusually large proportion” for the relatively quiet mid-summer period before a November election.

Voters are much less aware of Proposition 39, the Voter ID initiative. The measure would require voters at the polls to show government-issued identification; those who cast mail-in ballots would need to give the last four digits of a government-issued ID.

The split on voter ID in California appears to reflect sentiment nationwide on an issue that conservatives have been pressing for decades.

Among Republican likely voters, 93% favored Proposition 39’s ID requirements. Among Democrats, 80% would vote no. Among likely voters with no party preference, 54% opposed  Proposition 39.

A Berkeley IGS Poll released separately on Aug. 13, 2026, found Becerra backed by 55% of likely voters, a comfortable 18-point lead over Republican Steve Hilton. Becerra is a veteran California political leader who served as secretary of health and human services under President Joe Biden from 2021 to 2025. Hilton is a longtime political adviser in the U.K. and more recently a conservative political commentator and strong ally of President Donald Trump.

The poll was conducted online in English and Spanish from Aug. 3 to Aug. 9 among 4,207 registered voters throughout California. The poll has a margin of error of 2.5 percentage points.

The Institute of Governmental Studies is an interdisciplinary organized research unit at UC Berkeley, advancing an ambitious program of research, education and public service.

Source: UC Berkeley Institute of Governmental Studies.