On 3 November 2026, alongside the widely watched U.S. midterm elections, California held a referendum vote on Proposition 40, which proposes a one-time 5% wealth tax on net assets exceeding $1 billion for residents as of 1 January 2026.
:The LA Timesreported that this billionaire tax measure was driven by the Service Employees International Union (SEIU), specifically its United Healthcare Workers West division, supported by labor groups and some progressives including Vermont Senator Bernie Sanders.
The campaign began by collecting over 1.5 million registered voter signatures, surpassing the legal threshold required for citizen-initiated ballot measures.
Supporters argue that the tax is essential to aid disadvantaged groups and that billionaires have the capacity to pay it.
Opponents contend the tax would stifle innovation and incentivize wealthy individuals to leave the state, negatively impacting California’s fiscal revenue. Notably, Sergey Brin, Google’s co-founder, donated over $100 million to groups opposing the tax.
The battle over the tax measure is not just between supporters and opponents; simultaneously, Propositions 41 and 42 have been introduced to obstruct Proposition 40’s tax collection.
Proposition 41 aims to prohibit the state from enforcing tax laws enacted after 1 January 2026 that generate revenue exceeding state spending caps, and mandates independent audits of programs funded by new taxes. Proposition 40, however, allows revenues to be allocated to public health and social needs even if they exceed spending caps.
Proposition 42 seeks legal exemptions preventing the state from imposing new taxes on retirement accounts, savings, digital assets, financial instruments, or personal property.
Furthermore, Proposition 42 includes a ban on retroactive taxes, directly opposing the retroactive tax mechanisms authorized by Proposition 40.
Efforts to impose wealth taxes have varied globally. Some countries like Norway, Spain, Switzerland, and Colombia still apply them, while others such as Germany, Sweden, Austria, and France have repealed such measures.
This indicates no one-size-fits-all formula; effective tax policy requires careful design of tax bases, asset valuation, exemptions, and regulations tailored to each country’s context.
For Thailand, this case can be instructive, as the main impetus behind Proposition 40 is to raise revenue to support and stabilize healthcare programs. This aligns with Thailand’s National Health Security Fund under the National Health Security Office, which faces fiscal pressures from an aging population and rising medical and technological costs.
The latest vote count report as of 6 November 2026 byAssociated Press (AP)indicates that about 64% of all ballots have been counted. The election outcome remains officially undecided.
However, overall trends show opponents (No) leading with approximately 54%, or about 4.7 million votes.
Sources:Los Angeles Times, AP News,CNBC,Financial Times
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