Proposition 40 would impose a one-time tax of 5% on the assets of California billionaires, including wealth held in stocks and other investments. Its sponsor, SEIU-United Healthcare Workers West, estimates it would raise about $100 billion over five years, with most of the money intended to offset federal health-program cuts, including pressure on Medi-Cal.

The measure’s supporters say local endorsements show that union members and their leaders are divided over how to respond to wealth inequality and potential health-care funding losses. Statewide groups opposing Prop. 40 argue it could prompt billionaires to leave California, eroding income-tax revenue and public funding.

Among the local unions backing the measure are United Educators of San Francisco, which represents about 6,500 teachers and staff, and United Teachers Los Angeles, whose membership is about 35,000. Both have diverged from the California Teachers Association, a powerful statewide union that opposes Prop. 40.

Alex Schmaus, a political organizer for the San Francisco union, called the CTA’s opposition “an error” and said his local’s leadership endorsed the measure unanimously. “We’ve got to find a way to take on these billionaires,” he said.

The CTA has said it does not believe Prop. 40 would provide lasting funding for schools and communities. Its leaders have also raised concerns that voters could be confused by multiple tax measures on the November ballot. The CTA supports Proposition 3, which would permanently extend an existing tax on top-income earners that helps fund schools. Schmaus said he expects voters concerned about wealth inequality to support both measures.

A similar disagreement has emerged among construction unions. The statewide California Building & Construction Trades Council opposes Prop. 40, while supporters include the San Diego Building Trades Council, representing more than 35,000 workers, and Sheet Metal Workers’ Local 104, with about 10,000 members in the Bay Area and Northern California.

Vince Sugrue, the sheet metal workers’ state legislative director, said support among his members was “very overwhelming,” adding that health care was too important an issue for the union to stay out of the debate.

Chris Hannan, president of the statewide building trades council, said the organization’s members are not broadly rebelling. “The majority of our members are not revolting on this; the majority of our members are no on 40,” he said. Hannan said the council fears the tax could ultimately reduce revenue for infrastructure and school construction projects that provide union jobs.

The California Teachers Association, the building trades council, and unions representing firefighters and domestic workers oppose the measure. The California Labor Federation, the California Federation of Teachers, the California Nurses Association and the National Union of Healthcare Workers have endorsed it. The federation’s leader, Lorena Gonzalez, said the recent local endorsements reflect a “ground-up movement.”

The dispute comes as voters appear closely divided. A recent Citrin-POLITICO poll found 46% of likely voters supported Prop. 40 and 43% opposed it. A Stanford economists’ study estimated the tax would bring in about $30 billion while potentially costing California $39 billion in income-tax revenue over time if billionaires left the state. Those figures contrast with the larger revenue projection from the measure’s sponsor.

SEIU-UHW and its leader, Dave Regan, have faced criticism from other unions for developing the proposal without broader labor input. Critics also argue that only a small portion of its revenue would go to schools. Supporters counter that the measure is preferable to inaction, particularly as California faces uncertainty over health-care funding.

With Election Day set for Nov. 3, the growing divide between local union chapters and statewide leadership could matter in a contest where the electorate is narrowly split.