Tech billionaires have been dumping hundreds of millions of dollars into the fight against a wealth tax in California. They’ve raised more than $340m, and the campaign they’re funding is spending more than $1m a day to defeat the measure, according to state financial disclosures.

With the election less than a month away, those funds are being spent at a stepped-up pace. During the first 19 days of September, according to the most recent campaign filings, the opposition campaign plowed through at least $21.2m to fight the billionaire tax – surpassing $1m per day. Voters are being inundated with robotexts, mailers and advertisements that warn a tax on billionaires would “expose all Californians to higher taxes”, as one ad reads.

Californians will vote on the ballot measure, Proposition 40, in early November. If passed, it would require a one-time 5% tax on the state’s billionaires, with the proceeds mostly funding healthcare programs, along with some education and food assistance. The measure has divided Democrats in the state, with some giving enthusiastic support and others rejecting the proposal because it’s just a one-time levy and the bulk of it would only fund certain healthcare programs.