Salesforce chief executive Marc Benioff has escalated his attacks on fellow San Francisco billionaires, saying they are “hoarding” money and don’t want to help the homeless.

In an interview with the Guardian on Tuesday, the tech entrepreneur criticised payments company Stripe, which was founded by Limerick brothers John and Patrick Collison, for opposing Proposition C, a ballot measure that would tax large businesses in San Francisco by implementing an average 0.5 per cent gross receipts tax for company revenues over $50 million (€43 million). The measure is meant to help fix a rapidly expanding humanitarian crisis in the city.

The growth of tech firms such as Salesforce, a cloud computing company and one of the largest employers in the city, has contributed to a massive housing shortage, with thousands left homeless, including one in 25 public school children. Prop C, which Mr Benioff is backing, is expected to raise between $250 million and $300 million a year to pay for housing, shelters, mental health treatment and more.

Stripe claimed the measure lacked a “comprehensive plan” for spending in a recent op-ed and has also given more than $400,000 to a campaign fighting the measure, making it the largest donor.

Mr Benioff scoffed at the funding from Stripe, which was recently valued at $20 billion.

“It’s the most money they’ve ever given to anything in San Francisco, so that’s exciting . . . [Prop C] will be a direct tax on Stripe that they don’t want to have to pay,” he said. “Even though they’ve made $20 billion in San Francisco, they’re not willing to give back at scale. Isn’t that amazing?”

Patrick Collison, Stripe’s chief executive, did not respond to a request for comment. Ted Ladd, a spokesman, said that Stripe earlier this year gave a larger donation to California Yimby, a political group with tech funding that advocates for the construction of more housing in the state.

Mr Benioff also intensified his criticisms of Jack Dorsey, the chief executive of Twitter, saying: “He just doesn’t want to give, that’s all. And he hasn’t given anything of consequence in the city.”

Opposition

Mr Dorsey, who also runs Square, a second major San Francisco-based tech firm, recently announced his opposition to the measure, saying he did not believe it was “the best way” to “fix the homeless problem”.

Mr Benioff said by phone that he had expected Mr Dorsey to stand against Prop C – and that he did not anticipate the Twitter co-founder would change his mind or give back in a meaningful way.

“That’s not a surprise to me. There’s lots of chief executives and companies and billionaires in that category. We have 70 billionaires in San Francisco [Bay Area region]. Not all of them are giving money away. A lot of them are just hoarding it. They’re keeping it. That’s just who they are and how they look at their money.”

He continued: “This is a critical moment where I think Prop C kind of illuminates who is willing to be a San Franciscan and actually support our local services.”

Twitter has long received a massive tax break to operate in San Francisco. A Twitter spokesperson declined to comment on Tuesday.

Mr Benioff’s recent efforts to call out ultra-wealthy business leaders has caused divides in the tech industry, which has typically been united in its resistance to taxes that could fund services and combat income inequality.

Mr Benioff has pledged to donate at least $2 million to support Prop C, which could cost Salesforce up to $10 million a year in taxes. The philanthropist has developed a reputation as a social activist and liberal tech leader over the years, though he has recently faced significant backlash for his company’s contract with US Customs and Border Protection, an agency carrying out Donald Trump’s anti-immigrant agenda.

His decision to be outspoken on Prop C has earned him some praise from progressive activists, especially since the city’s mayor, London Breed, recently announced her opposition. The Democratic mayor expressed concern about the “flight of headquarter companies” and “jobs” if Prop C passed, a claim that put her in an awkward position after Mr Benioff became a vocal supporter of the measure.

Mr Benioff said that Ms Breed had recently asked him for an “immediate $8 million” to fund a shelter in the city, raising questions about her claims that the city needs to focus on auditing the $300 million it currently spends on homelessness instead of raising new money.

“She wants me to fund personally a homeless shelter in the city, because she’s out of cash,” he said. “That’s evidence we need more money now.”

Risk

He said it appeared that the mayor had decided Prop C is “just a risk she can’t take”. The mayor’s spokeswoman did not respond to questions about the reported $8 million request, but sent a statement from Ms Breed, saying: “I do not believe doubling what we spend on homelessness without new accountability, when we don’t even spend what we have now efficiently, is good government.”

Mr Benioff said over the years he has learned that there are two kinds of wealthy San Franciscans – “people who are willing to give and people who are not willing to give”, adding: “When it comes to this Proposition C, it’s the same two buckets. You’re either for the homeless or you’re for yourself.” – Guardian service