The CEOs of two of the world’s most prominent tech companies got into an online spat on Friday over who was doing the most to address homelessness.

The Salesforce CEO, Marc Benioff, and Twitter CEO, Jack Dorsey, were tweeting at each other about a proposed tax on high-earning San Francisco businesses. It would redirect millions of dollars to help thousands of people who live on the streets, including outside the headquarters of both companies.

Benioff tweeted that he was in favor of the tax. Dorsey tweeted that he was not – prompting a displeased response.

“Hi Jack. Thanks for the feedback,” Benioff quipped. “Which homeless programs in our city are you supporting? Can you tell me what Twitter and Square & you are in for & at what financial levels? How much have you given to heading home our $37M initiative to get every homeless child off the streets?”

Benioff was referring to an initiative he is spearheading for homeless families. In May he announced that he and his wife would match a $1.5m donation from his company’s philanthropic arm.

In a second tweet, he alleged that Dorsey had failed to contribute to the city’s homeless programs, public hospitals and public schools, despite earning billions and receiving a tax break to relocate in a deprived part of town.

Dorsey did not respond. He has taken on the housing crisis in different ways, and recently threw his weight behind a controversial bill that would have made it more difficult for cities to say no to development.

Both billionaires have grown their businesses in the heart of San Francisco, where roughly 7,500 people sleep on the sidewalks each night. The tech boom has contributed to rising housing costs that have exacerbated the problem.

Tech industry moguls have come under fire in their past for their responses to homelessness, from supporting a controversial proposition, passed in 2016, restricting tents on sidewalks, to public rants. One tech company founder referred to homeless people as “riff-raff” and complained about having to encounter them.

If voters approve the tax ballot measure, called Proposition C, next month, an estimated $250-$300m in additional revenue would go toward housing the homeless, providing rental assistance and bolstering mental health services and shelters. According to an analysis conducted by the city’s Office of the Controller, about 300 to 400 businesses would be affected. Fifty percent of them would be in the information and financial services sectors.

A slew of left-leaning organizations and representatives, including the House minority leader, Nancy Pelosi, support the tax, but the newly elected mayor, London Breed, has come out against it, citing concerns that it could put a chill on economic growth.

“We all recognize the crisis on our streets; we see it every day,” she wrote on Medium. “So I understand why Proposition C sounds appealing, and I know those who support it are well-intentioned. But as Mayor, I must weigh more than popularity and good intentions. I must consider the long-term impacts on our City.”

Breed has been criticized for her position, especially now that Benioff – whose business will be among those expected to pay the tax – has become so vocal in his support.

“Homelessness is all of our responsibility which is why we are supporting Prop C,” he stated in a tweet now pinned to the top of his page. “Together, as one San Francisco, we can take on our city’s most complex & difficult problems. As SF’s largest employer we recognize we are part of the solution.”