Last spring, in an effort to spur economic growth in San Francisco, Mayor Edwin M. Lee and David Chiu, president of the Board of Supervisors, engineered legislation to waive millions of dollars in taxes for technology companies like Twitter and Zynga.

Now, with both men running for mayor, the tech industry is returning the favor.

Noah Berger for The Bay Citizen

San Francisco Board of Supervisors President David Chiu, left, and San Francisco Mayor Ed Lee cut a ribbon at Zendesk's Market Street offices on Aug. 30, 2011. At right is Zendesk CEO Mikkel Svane.

In late June, more than a dozen executives, including Ali Row-ghani and David Wehner — chief financial officers of Twitter and Zynga, respectively — hosted a $100-a-plate fundraiser for Chiu. The event, “Innovate SF,” brought in about $6,000, according to Chiu’s campaign.

Meanwhile, Ron Conway, a major investor in Twitter, aims to raise as much as $1 million for a political action committee that is expected to run television ads in support of Lee during the run-up to the Nov. 8 election, according to several San Francisco fundraisers.

Under federal election laws, Conway can independently solicit unrestricted amounts of money on Lee’s behalf. He has raised thousands of dollars over the past few weeks, city records show, including a $1,000 donation from Marc Benioff, the founder of Salesforce, and a $500 donation from Mortimer B. Zuckerman, the media and real estate mogul based in New York.

“Ron has seen how effective Ed Lee has been in just a few months as mayor,” said Brian Brokaw, a political consultant working for Conway. “He recognizes that Ed Lee is a public servant, not a career politician, and hasn’t spent years accumulating a campaign war chest, so he’s committed to raising and contributing his own resources to support Ed Lee.”

Silicon Valley has exerted a powerful pull over national and state politics for more than a decade, but the mayoral campaigns for Lee and Chiu show how a new wave of booming startups in San Francisco has emerged as a major force on the local level as well.

The industry is realizing its political might in a variety of ways.

In March, Twitter negotiated a payroll tax exemption worth more than $30 million by agreeing to move into the blighted Central Market neighborhood, which officials hope to develop. Two months later, Zynga pressured the city into granting a separate tax break for companies that go public within the next two years.

Conway spent $35,000 to support the controversial sit-lie initiative, which passed last November. Michael Moritz, a partner at Sequoia Capital and one of the world’s pre-eminent venture capitalists, jolted San Francisco politics last year when he spent more than $250,000 to support a pension reform initiative that was bitterly opposed by unions and most of the political establishment. That measure failed, but Moritz now supports another pension reform effort, as well as the mayoral campaign of Jeff Adachi, the public defender.

“By far and away the biggest issue confronted by people from the tech industry — and it completely dwarfs the sit-lie/payroll/stock options stuff is pension reform,” Moritz said in an email. “Whichever pension measure passes this fall, San Franciscans can thank Silicon Valley. Without pressure from the tech industry, San Francisco would just be closer to the abyss.”

Other tech veterans are experiencing firsthand success in San Francisco elections, an insular arena traditionally dominated by Democratic Party bosses, union leaders and entrenched political families. Mark Farrell, a venture capitalist, was elected to the Board of Supervisors in November. Another, Joanna Rees, is now one of a dozen leading candidates for mayor.

Chiu and Lee acknowledge that the growing industry represents a vast pool of young, wealthy voters. But their support, they say, is rooted in the fact that employment in San Francisco’s tech industry has shot up 60 percent since 2005, to more than 30,000 jobs.

“The reason why David and I are so passionate about tech is because they offer jobs,” Lee said in an interview. “That’s why we support them in the city, and that’s why we’re giving a lot of attention to startups. I’m not looking at it in terms of votes.”