Gov. Gavin Newsom vowed to stop California's billionaire tax. He has just over a week left to keep it off the ballot.

Gavin Newsom’s fight to stop a proposed tax on billionaires in California is coming down to the wire.

The so-called billionaire tax — which would impose a one-time 5% tax on California residents whose assets exceed $1 billion — could appear on the ballot this November if critics aren’t able to stop it ahead of a June 25 deadline.

Newsom previously vowed to fight the proposed tax, telling The New York Times in January he believed it would hinder innovation. “I’ll do what I have to do to protect the state,” he said.

The measure was proposed by SEIU-UHW, a healthcare workers union, which announced in April that it had submitted 1.55 million signatures, nearly double the roughly 875,000 needed.

The deadline for initiative measures to qualify for the November ballot is June 25.

With the deadline approaching, several California groups that generally align with Democrats are coming out publicly against the initiative and pressuring proponents to withdraw the measure.

The California Teachers Association — one of the state’s largest teachers unions — voted to oppose the tax, saying it would not provide sustainable funding for schools and communities.

Planned Parenthood Affiliates of California and several other labor groups have also come out against it.

The measure has the support of progressive Rep.

Ro Khanna, the labor union Teamsters California, and the California Democratic Socialists of America.

If the measure qualifies, voters would decide in November whether California should impose the one-time tax on its wealthiest residents.

Because it’s a ballot measure, Newsom would not have the power to veto it.

Supporters say the tax would raise money primarily for healthcare, as well as education and food assistance programs.

Opponents say it could drive billionaires — and future tax revenue — out of the Golden State.

Business Insider previously reported that, as of January 1, California had over 200 billionaires who could be affected by the tax.

Some wealthy residents have already made moves out of the state, including Google cofounder Larry Page.

However, not all billionaires are in opposition.

Nvidia CEO Jensen Huang said he was “perfectly fine” with the tax.

Newsom’s office and SEIU-UHW did not respond to requests for comment from Business Insider.