Proposal to introduce one-time tax of 5% will go to voters in November after backers decline to withdraw measure California’s billionaire tax, explained: what you need to know California voters will get to decide in November whether billionaires should pay a one-time 5% tax, after a deadline passed on Thursday for its backers to withdraw the measure. The so-called billionaire tax is among the highest-profile ballot efforts in the US this year taking aim at rising wealth disparities, and is set to be one of the state’s most contentious ballot initiatives. It has already spurred tech moguls to pour millions of dollars into attempts to stop the proposal.