LOS ANGELES -- California's Democratic Party has endorsed the state's proposed billionaire tax, marking a win for its advocates three months before Californians vote on the measure.

At a weekend meeting of hundreds of party officials, the tax proposal on Sunday cleared the 60% threshold needed to overcome objections and win the endorsement, according to a party spokeswoman. California voters will decide whether to approve or reject the ballot initiative in November. If it takes effect, the state's roughly 200 billionaires would pay a 5%, one-time levy.

The support of state Democratic officials gives the proposed levy a public-relations boost that was far from assured. The tax has sharply divided the party establishment, with Democratic Gov. Gavin Newsom and Democratic gubernatorial candidate Xavier Becerra publicly opposed to it.

The proposal was initiated by a large healthcare union. Several billionaires and some other unions opposed the tax. Both sides mounted fierce lobbying campaigns to sway executive board members at the state Democrats' meeting this weekend.

"This endorsement puts to rest the idea that California Democrats are not united by the billionaire tax -- they are," said Dave Regan, president of the Service Employees International Union United Healthcare Workers West, which proposed the initiative.

Independent polling has shown a strong majority of Democratic voters in California and a narrower majority of the broader electorate support the tax. The SEIU-UHW proposed the tax to try to raise $100 billion aimed mostly at offsetting the Trump administration's deep healthcare funding cuts.

Progressive leaders including Sen. Bernie Sanders (I., Vt.) and U.S. Rep. Ro Khanna (D., Calif.) have backed the proposal, saying the health funding is needed and that the wealthiest Californians should be paying more.

Newsom, a Democrat seen as a potential 2028 presidential candidate, has argued that the levy could push the state's largest taxpayers to flee. Other opponents include the California Teachers Association and California Professional Firefighters.

After the tax initiative qualified for the ballot in June, the governor and his allies fought to persuade the SEIU-UHW to withdraw it. The union at one point offered to withdraw the proposal in exchange for Newsom backing a smaller wealth tax.

The tax would apply to people who resided in California as of Jan. 1 of this year and who have a net worth of $1 billion or more at the end of this year. A person's net worth excludes certain assets, such as real estate they own directly, for purposes of the tax.

Members of the California Democratic Party's roughly 380-member executive board gathered this weekend in San Diego to consider various proposals on the November ballot.

In a sign of how divisive the proposal has become in California, opponents and advocates scrambled to whip votes at a waterside Sheraton hotel near the airport.

The union hosted a hospitality suite with food and drinks, and set up a booth where members handed out T-shirts, hats and other swag touting the billionaire tax.

Opponents of the tax paid around $7,000 to cover hotel rooms, registration fees and travel expenses for several voting board members and their proxies, according to a person familiar with the matter.

The payments were made by the "No on Prop 40" campaign via Hilltop Public Solutions, a political consulting firm hired by opponents of the billionaire tax. The No on Prop 40 campaign is backed by the California Medical Association and California Primary Care Association Advocates. The first group didn't respond to requests for comment, and the latter referred questions to the campaign, which provided a statement from a Hilltop official.

"The No on 40 campaign provided limited travel assistance for a handful of volunteers and supporters who requested help offsetting costs -- a common practice for candidate and ballot campaigns," said Marco Meneghin, a principal at Hilltop, in the statement.

Following Sunday's vote, a spokesman for the No on Prop 40 campaign called the proposed billionaire tax "bad for our budget, bad for our economy and bad for our future."