Salesforce CEO Marc Benioff got into a Twitter beef with another exec over a controversial measure tackling San Francisco's homelessness crisis

Kimberly White/Getty Images for Fortun

• Proposition C is a ballot measure in San Francisco, California that would tax the city's largest corporations to provide more funding to homeless services. 
• On Saturday, the gloves came off over Twitter between Zynga chairman and co-founder Mark Pincus and Salesforce CEO Marc Benioff. 
• Pincus tweeted: "Prop c is the dumbest, least thought out prop ever."
• Benioff countered by asking: "Mark what's your plan & what's your contribution to helping our homeless?" 

As election day approaches, the gloves are coming off for some Silicon Valley execs over the controversial Proposition C, a ballot measure in San Francisco that would tax the city's largest corporations to provide relief in the city's ongoing homelessness crisis. 

The latest bout came Saturday between Zynga chairman and co-founder Mark Pincus and Salesforce CEO Marc Benioff - the latter of whom had previously taken Twitter CEO Jack Dorsey to task for his opposition to Prop C.

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Over the past two months, Benioff has become the undisputed top evangelist in support of Prop C, with him and his company donating a combined $7.9 million to the cause. That's put him at odds with figures including San Francisco Mayor London Breed, who vocally opposes Proposition C. 

Pincus, who according to public records has not donated to either side of the measure, tweeted on Saturday, calling Prop C, "the dumbest, least thought out prop ever." He questioned how much taxes would increase for Salesforce and Zynga should the proposition pass muster with voters, and said the proposed measure "doesnt connect the problem to the money in a logical way." 

Benioff said the homelessness issue in San Francisco was urgent and that,"we can not wait any longer for a 'better' or 'more fair' plan."

Here's how the conversation went down. 

Pincus' tweet set things off. 

Later that night, Benioff responded, setting off a short social media donnybrook.

Some back-of-the-envelope math ensued to better understand how much Salesforce would be paying in taxes under Proposition C - Benioff said it would range between $10-$11 million per year. 

Pincus shot back that it didn't matter how much Zynga would pay - he stood by Mayor Breed's position that it wouldn't help, no matter how much was raised by the measure. 

The two execs went back and forth: Pincus agreed with Benioff that business gives a new platform to effect change, but like many in opposition to Prop C, he believes there needs to be a better plan in place to fight homelessness in San Francisco. 

They eventually reached some kind of impasse. At 10:25 PT, Benioff walked away, revealing his Bitmoji to the world as he slammed the door on Pincus.

Read more: San Francisco's tech billionaires are fighting over how to deal with the city's homelessness crisis - Here's what each tech bigwig says about Tuesday's vote on Prop C

Benioff's own support for Prop C came by way of Twitter, after a late night direct message conversation with a San Francisco bookstore owner back in September convinced him to back the measure fully. Since then, Benioff has thrown all of his might behind the Prop C fight, urging fellow executives to back the measure. 

If passed, Prop C would bring in an additional $250 to $300 million annually to help fight homelessness in San Francisco. Mayor Breed and other critics say that the city's homelessness crisis can't be solved by throwing money at it, and that it could make things worse.