Attorney Alex Spiro wrote to California Gov. Gavin Newsom saying several of his clients would relocate if a billionaire tax were implemented. Ramsay de Give-Pool/Getty Images; Michael M. Santiago/Getty Images Attorney Alex Spiro wrote a letter to California Gov. Gavin Newsom, urging him to stop a proposed billionaire tax. Spiro said his clients would "permanently relocate" if the measure were to become law. While Spiro did not say which clients he was referencing, he has previously represented well known billionaires and celebrities. A proposed billionaire tax in California has the wealthy threatening to flee, according to a letter written by power lawyer Alex Spiro to Gov. Gavin Newsom. In a December 11 letter that was obtained by Business Insider, Spiro lays out his opposition to the proposed tax on behalf of his clients, who he calls "California residents who would be subject to the proposed Billionaire Tax Act." "It will trigger an exodus of capital and innovation from California," Spiro wrote. "Our clients have made clear they will permanently relocate if subjected to this tax." The measure proposes that California residents with assets exceeding $1 billion be subject to a one-time 5% tax on the value of their assets. If the proposal receives enough signatures, it will appear on the state ballot in November 2026. If passed, it would apply retroactively to all California residents as of January 1, 2026. While Newsom has said he is against the tax and would "fight" it, he would not have the ability to veto it if it were to pass as a ballot measure. Several wealthy Californians, including venture capitalist Peter Thiel and Google cofounder Larry Page, have considered shrinking their presence in California, according to a New York Times report. Representatives for Page and Thiel did not respond to Business Insider when asked if they were represented by Spiro. Over the weekend, billionaire Palmer Luckey took to X to voice his opposition to the measure. "I made my money from my first company, paid hundreds of millions of dollars in taxes on it," the Anduril cofounder wrote. "Now me and my cofounders have to somehow come up with billions of dollars in cash." While it's not clear which clients the lawyer was referencing in his letter to Newsom, Spiro's client roster in the past has included billionaires and A-listers. He has previously represented Kim Kardashian, Jay-Z, and Elon Musk. Read the full letter below: Re: Constitutional Concerns Regarding Proposed Billionaire Tax Act Dear Governor Newsom: I represent California residents who would be subject to the proposed Billionaire Tax Act if it qualifies for the November 2026 ballot. I write to urge you to work to prevent this initiative from moving forward. The Act has serious legal problems and would cause significant economic damage to California and the broader economy. First, and most importantly, the Act would be unconstitutional. Although the Act purports to be a tax, it is in reality an uncompensated confiscation of property. The Act imposes a 5% levy on total accumulated wealth, including illiquid assets that generate no income. That is in substance a taking without just compensation. As the Supreme Court explained in Armstrong v. United States, the government cannot force "some people alone to bear public burdens which, in all fairness and justice, should be borne by the public as a whole." 364 U.S. 40, 49 (1960). The Act concentrates an extraordinary burden on a small group to solve a general revenue problem— exactly what the Constitution prohibits. Second, for the people who relocate from California in 2026 before the November election, the Act would tax them after they have become citizens of other States and without any ability to vote on the measure. The Supreme Court has held that retroactive taxation cannot be "harsh and oppressive." United States v. Carlton, 512 U.S. 26, 30 (1994). A 5% levy on total net worth imposed on former residents who departed before the law was even enacted clearly meets that definition. Third, the Act's unprecedented novelty makes it especially vulnerable to a legal challenge. California has never imposed a wealth tax, much less one that reaches former residents and that is targeted at a small group of citizens. The Supreme Court closely scrutinizes unprecedented exercises of government power precisely because they lack historical precedent. See Biden v. Nebraska, 600 U.S. 477, 505 (2023). In fact, it has not hesitated to invalidate the retroactive application of new taxes, even for far less extreme measures. See Blodgett v. Holden, 275 U.S. 142 (1927). There can be no doubt that the current Supreme Court would carefully evaluate a law so out of step with the American legal tradition. From an economic perspective, the Act creates two serious problems. First, it will trigger an exodus of capital and innovation from California. Our clients have made clear they will permanently relocate if subjected to this tax. They are not alone. See California's wealth-tax test: Have voters finally found a policy that the state's inherent economic strengths can't overcome?, Wash. Post (Nov. 17, 2025) (opinion) (describing the tax as "almost tailor-made to drive most Silicon Valley tech companies to Austin, Texas"). In other words, by passing this proposal California would exchange a one-time windfall for the permanent loss of billions in annual income taxes, capital gains taxes, property taxes, and economic activity. The state's most economically productive residents would take their businesses, jobs, and charitable giving with them. Second, the Act will force destructive asset sales. Our clients hold equity stakes in operating businesses, venture capital funds, and real estate. Paying a 5% wealth tax would require massive forced liquidations, depressing asset values and triggering market instability that would harm ordinary investors whose retirement accounts hold these same investments. Our clients are prepared to mount a vigorous constitutional challenge if this measure advances. Litigation would be protracted and expensive, and it would generate sustained negative attention to California's business climate. The prudent course is to prevent this constitutionally defective measure from reaching the ballot. We respectfully ask that you discourage signature gathering, oppose qualification, and if necessary, campaign against passage. 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. We hope this can be resolved through political channels rather than through years of contentious litigation. Respectfully, Alex Spiro Read the original article on Business Insider