Fact check: Could California lawmakers expand the billionaire tax to everyone?

Opponents of Proposition 40 have a message for voters: Don’t be fooled. The billionaire tax is a “Trojan horse” for new taxes on all Californians, ads proclaim. But is that true?

Tucked into the initiative is language granting the Legislature authority to amend the tax by a two-thirds vote “if the statute is consistent with and furthers the purposes of the 2026 Billionaire Tax Act.” Opponents argue lawmakers and a future governor could, with the stroke of a pen, expand the wealth tax to people with far less than $1 billion.

In a high-tax state, that argument could hold a lot of sway with voters.

Service Employees International Union-United Healthcare Workers West put Prop. 40 on the ballot; the initiative would levy a one-time, 5% tax on billionaire’s assets. The union rejects the premise of the ad. It says the tax is limited to billionaires and any legislative amendment would have to hew closely to that purpose. Dave Regan, president of SEIU-UHW, said opponents’ ads are pure scare tactics.

“The billionaire tax is a tax on billionaires. Period. If you’re not a billionaire, you don’t pay the tax,” Regan said in a statement to CalMatters.

Rob Lapsley, president of the California Business Roundtable, the group that paid for the ad, said the message was meant to highlight the policy implications of a wealth tax and the power Prop. 40 gives lawmakers.

“Californians deserve to understand those issues and what they could mean for taxpayers and the state’s economy,” Lapsley said in a statement.

A separate, billionaire-backed group opposed to Prop. 40 has also said the initiative “gives politicians the power to expand the tax to anyone.”

The truth lies somewhere in between.

California courts have given lawmakers real authority to amend laws created by ballot initiatives if the original text of the initiative permits it. However, that power is not unlimited and the measure includes language restricting future legislative changes, said Michael Colantuono, an attorney with expertise in state election law.

Opponents’ ads also don’t mention that Prop. 40 writes the tax into the state Constitution, not just state law, so expanding it would require another trip to the ballot.

Legislative authority

Legal experts agree that if Prop. 40 passes, lawmakers would be able to make certain amendments without taking it back to voters.

The state Constitution allows the Legislature to amend a ballot initiative without another vote if the initiative permits it. That’s a relatively common clause in ballot measures, and Prop. 40 includes it.

Megan Jones, a tax attorney at Holland & Knight, said proponents’ claims that the tax could never be changed are disingenuous.

“If it’s going to further the purposes, then they could,” Jones said.

For example, voters passed the Political Reform Act, which governs campaign finance and lobbying rules, in 1974 and lawmakers have amended it almost continually since.

Similarly, lawmakers have amended the Mental Health Services Act, a voter-approved 1% income tax on millionaires, 10 times since its passage in 2004. None of those amendments adjusted the tax rate. Most recently, lawmakers voted to substantially alter how the state spends mental health money and raise additional bond funds. Those changes went back to voters in 2024 as Proposition 1.

But there isn’t always a clear line for when voters need to approve changes, experts say.

“It is common for the Legislature to make amendments,” Colantuono said. “It is (also) common for there to be disputes about those amendments.”

‘Furthers the purposes of’

“Ultimately, it ends up in court,” said Chris Parker, a principal tax attorney at the firm Baker Tilly.

The California Supreme Court ruled in a 1995 case that the Legislature may amend voter-approved laws if the changes can be interpreted as furthering voters’ original goals “by any reasonable construction” — giving lawmakers broad latitude.

In 2021, the state Supreme Court held that the Legislature appropriately amended Proposition 57, a criminal justice reform measure, by barring the transferring of minors under 16 to adult court. Justices cited the 1995 case, noting that “a strong presumption of constitutionality supports the Legislature’s acts.”

Still, the language of the proposition matters.

A few years earlier, in 2019, the Third District Court of Appeal held that a legislative attempt to allow public funding of political campaigns “directly conflicts with a primary purpose” of the Political Reform Act. Lawmakers responded by passing a new bill asking voters to weigh in directly — it appears on this year’s ballot as Proposition 4.

Judges look at two things, Coluantuono said: what reasonable voters thought they were approving, and whether later legislative changes helped that goal, or got in the way.

Certain provisions of Prop. 40 would make it difficult for lawmakers to expand the tax beyond billionaires. The 1995 case established that courts may weigh the language of a ballot measure, arguments printed in the voter guide, and historical context when deciding whether change is consistent with voter intent.

Prop. 40’s purpose and intent section says the measure is meant to support healthcare and education “by raising revenue from a one-time tax on billionaire wealth” — referencing billionaire wealth three times. The voter guide arguments similarly target “approximately 200 California billionaires.”

“They could probably adjust the structure of the tax in marginal ways, but what they couldn’t do is make it a more than a one-time tax, and they probably couldn’t lower the threshold on wealth,” Coluantuono said.

A separate concern: how do you prove wealth?

Should Prop. 40 pass, it would create an entirely new tax structure in California — one that assigns a value to very wealthy people’s investments, public and private businesses, as well as personal property such as art or car collections.

Valuing something like a tech startup that hasn’t produced a product or gone public could prove especially difficult, Parker said.

“The excise tax that’s being proposed here is on potential,” he said. “The question then is, if we open the door to taxing potential, when does that stop?”

Lawmakers have periodically tried to pass wealth taxes, but the bills quickly stalled. This marks the first time voters will directly decide on one, making Prop. 40 a crucial test of how much appetite Californians have for his kind of tax structure. Jones said the bigger worry isn’t the tax itself, but other taxes that could follow.

“It’s a slippery slope,” she said.

Coluantuono said it would still be politically risky for lawmakers to try to implement a wealth tax on everyday Californians, but history shows temporary taxes have more than once become permanent.

“When we get a revenue stream in the government and we start spending it on services that people value… there’s tremendous political pressure to prevent the sunset,” he said.

Supported by the California Health Care Foundation (CHCF), which works to ensure that people have access to the care they need, when they need it, at a price they can afford. Visit www.chcf.org to learn more.