Elon Musk’s attorney Alex Spiro is the latest billionaire rep to blast a proposed California wealth tax that has some of the state’s wealthiest residents heading for the exits — with the power lawyer urging Gov. Gavin Newsom to scrap the idea.

The billionaire tax “will trigger an exodus of capital and innovation from California,” Spiro wrote in a Dec. 11 letter to Newsom, which was obtained by Business Insider and confirmed by The Post.

“Our clients have made clear they will permanently relocate if subjected to this tax,” Spiro wrote on behalf of unnamed billionaire clients.

Spiro, Musk’s longtime attorney who is representing the X owner in an ongoing shareholder lawsuit, asked Newsom to help kill the proposed 5% wealth tax on billionaires or face a painful legal challenge and embarrassing press coverage.

“Our clients prefer to remain in California and continue contributing to the state’s economy and civic life. But they will not remain if subjected to an unconstitutional confiscation of their wealth,” Spiro wrote.

“We hope this can be resolved through political channels rather than through years of contentious litigation,” Spiro continued.

Even Newsom is on record opposing the billionaire tax, a voter initiative sponsored by SEIU-United Healthcare Workers West union that needs about 870,000 signatures to qualify for the November 2026 ballot.

Although Newsom has no direct authority to stop the tax, Spiro suggested he “discourage signature gathering, oppose qualification, and if necessary, campaign against passage” to prevent an exodus of capital and wealth from California.

It’s not clear who Spiro is speaking for in the letter; the celebrity lawyer has repped rappers Jay-Z and Megan Thee Stallion, and New England Patriots owner Robert Kraft, in addition to handling various matters for Musk.

Google co-founder Larry Page, venture capitalist Peter Thiel and investor Chamath Palihapitiya are among the California billionaires potentially preparing to flee California before the end of the year.

Page and Thiel could be on the hook for roughly $12 billion and $1.2 billion, respectively, under the proposed billionaire tax.

Musk, who founded multiple companies in California before moving to Texas in 2020, has had a tumultuous relationship with the Golden State and its governor.

After growing Tesla and SpaceX in California, tensions arose when Musk defied the state’s strict Covid lockdowns. Newsom later said he wasn’t “worried” about Musk leaving the state.

“I’ve had a lot of conversations with him, and we’re committed to the success and the innovation and the low-carbon, green-growth economy that he’s been promoting for decades and the state of California is accelerating in,” Newsom told CNBC in May 2020.   

The two appeared together at an event celebrating a new Tesla AI and engineering site in 2023, but later sparred more recently as Musk grew increasingly critical of California regulations and liberal politics.

Musk and Newsom clashed earlier in December after the governor’s press office posted, “We’re sorry your daughter hates you, Elon,” in response to Musk’s America PAC knocking Newom’s support for pro-trans bills in California.

“I assume you’re referring to my son, Xavier, who has a tragic mental illness caused by the evil woke mind virus you push on vulnerable children,” Musk shot back on X.

Spiro argued in his letter to Newsom that the proposed billionaire tax is an illegal confiscation of property and would force taxpayers to liquidate assets en masse.

Moreover, it would “exchange a one-time windfall for the permanent loss of billions in annual income taxes, capital gains taxes, property taxes, and economic activity” — echoing other critics who say the tax would backfire, killing the Golden Goose.