Almost half of California’s personal income tax revenue comes from the state’s top 1% of earners. A proposed billionaires’ tax in California has ignited a political uproar in Silicon Valley, with tech titans threatening to leave the state while Democratic Gov. Gavin Newsom maneuvers to defeat a levy that he fears will lead to an exodus of wealth.A technology mecca, California has more billionaires than any other state — a few hundred, by some estimates. Nearly half its personal income tax revenue, a financial backbone in the nearly $350 billion budget, comes from the top 1% of earners.A large health care union is attempting to place a proposal before voters in November that would impose a one-time 5% tax on the assets of billionaires — including stocks, art, businesses, collectibles and intellectual property — to backfill federal funding cuts to health services for lower-income people that were signed by President Donald Trump last year.In a state with a vast gap between rich and poor, the plan has resulted in a tangle of competing interests at a time when both Democrats and Republicans are struggling to respond to economic anxiety driven by rising costs ahead of this year’s midterm elections.An online war of words has tech leaders pondering a hollowing out of Silicon Valley, and millions of dollars are flowing to political committees engaged in the fight. That includes $3 million from billionaire Peter Thiel, a founder of PayPal, to a committee tied to a business group opposing the tax.However it’s not clear if the proposal will make the ballot, with more than 870,000 petition signatures required for it to qualify.