Californians are facing a pivotal vote on Proposition 40, a ballot measure that could significantly alter how the ultra-wealthy are taxed. Known as the "billionaire tax," the proposal would impose a one-time 5% levy on the assets of approximately 250 billionaires residing in California. If enacted, it would represent the first wealth tax in the United States specifically aimed at billionaires, potentially setting a precedent for similar legislation in other states and at the federal level.
Supporters, including the SEIU-United Healthcare Workers West union, estimate the measure could generate $103 billion to address a state funding shortfall exacerbated by federal cuts to healthcare and food assistance. Billionaires would have the option to pay the tax as a lump sum in 2027 or in annual installments of 1% of their wealth over five years. However, the proposal faces significant opposition, including rival ballot initiatives and extensive advertising campaigns funded by wealthy individuals.
Billionaires have reportedly spent upwards of $180 million to oppose Proposition 40, arguing that such a tax would incentivize wealthy residents to leave the state, thereby diminishing its tax revenue over time. Some prominent Democrats, including Governor Gavin Newsom, have echoed these concerns, worrying about potential business departures from California. Conversely, progressive figures like Senator Bernie Sanders (I-Vt.) and Representative Ro Khanna (D-Calif.) have actively supported the measure.
A September poll from UC Berkeley indicated a divided electorate, with 45% in favor of the tax, 42% opposed, and 13% undecided. Opponents are expected to ramp up their spending, while SEIU-UHW is mobilizing with phone banking and door-knocking efforts.
Economic Disparities and Tax Challenges
Economists estimate that the wealth of California's billionaires has seen a substantial increase, growing by 144% between 2023 and 2025, far outpacing the 17% growth in adjusted gross income for all California residents during the same period. As of mid-2026, the combined wealth of the state's billionaires is estimated to be around $2.3 trillion, equivalent to half of the state's annual GDP. This disparity is partly attributed to the nature of billionaire wealth, which is often held in unrealized capital gains and not taxed until assets are sold. Wealthy individuals can also borrow against these assets and pass them to heirs tax-free.
Research indicates that the wealthiest Americans pay a lower effective tax rate compared to other income brackets. Between 2018 and 2020, the country's wealthiest billionaires paid approximately 24% of their income in state, local, and federal taxes, while other U.S. taxpayers paid around 30%. From 2023 to 2025, billionaires in California are estimated to have paid only 0.2% of their wealth in annual state income taxes. Advocates argue that measures like Proposition 40 are necessary to address this significant imbalance and the growing economic inequality.
Meanwhile, many working-class Californians are experiencing financial strain due to rising costs of living. Federal tax policies, such as President Trump's One Big Beautiful Bill Act, have been criticized for extending tax breaks for the wealthy and cutting social program funding, potentially leading to significant cuts in California's Medi-Cal program. Supporters of Proposition 40 state that the tax is intended to offset such impacts.
Contentious Support and Opposition
The proposal has created unlikely divisions, with some progressives favoring a recurring tax on unrealized capital gains rather than a one-time boost. Critics argue that Proposition 40 is a missed opportunity for more sustainable, systemic changes. However, proponents contend that the one-time tax is the most politically feasible option, especially given the political climate favoring tax breaks for the wealthy.
Opposition has also manifested in competing ballot measures, Proposition 41 and Proposition 42, which could nullify Proposition 40 if they receive more votes. Billionaires, including Google co-founder Sergey Brin, have heavily funded these initiatives. Brin, a friend of Governor Newsom, has also moved to establish ties in other states, a common tactic among those seeking to avoid potential new taxes.
While opponents argue that such taxes lead to capital flight, past research suggests that significant tax-driven migration among millionaires is rare. Analyses from the Hoover Institution suggest California could lose billions in revenue, while the nonpartisan Legislative Analyst's Office estimates potential annual losses under $1 billion, a fraction of the state's income tax revenue. Proponents also note that venture capital investment in California has continued to grow despite the threat of the tax.
Internal disagreements also exist among progressive groups. The California Teachers Association opposes Proposition 40, advocating instead for an extension of existing state taxes. Planned Parenthood of California has also expressed concerns about the potential impact on the state budget and fund allocation.
Broader Implications
If passed, Proposition 40 could serve as a catalyst for similar wealth taxes in other states and elevate the national conversation around taxing the ultra-wealthy. Public opinion generally favors higher taxes on corporations and high-income earners, with growing concerns about economic inequality and the influence of wealthy individuals on the political system.
California's history of pioneering progressive policies, such as paid family leave and data privacy regulations, positions it as a potential trendsetter for wealth taxation. Similar measures, including a millionaires tax in Washington state and a "pied-à-terre" tax in New York City, reflect a broader trend of confronting the financial contributions of the wealthiest.
At the federal level, proposals for an annual levy on billionaires have been introduced, aiming to fund social programs. The outcome of California's Proposition 40 is seen by supporters as a significant indicator of voter sentiment on these issues, with national and global attention focused on its potential impact.