LOS ANGELES (AP) — 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.