Here come the IPOs and here comes a proposal to tax them...

A lot of San Francisco companies are preparing to go public, and one city supervisor wants to tax them to offset the “negative impacts” that the sudden injection of wealth is expected to have on the city.

Supervisor Gordon Mar’s solution is a proposed tax on stock-based compensation that he revealed Wednesday.

“This is an important moment for us as a city to really reflect on what has played out in the last decade with the tech boom,” he said. “And how that has played such a direct and indirect role in so many of the challenges that we are having to grapple with in the city, whether that’s affordability or traffic congestion.”

Mar proposed placing a 1.12% payroll tax on stock-based compensation on the November ballot. Combined with the existing 0.38% payroll tax rate, the new tax would restore San Francisco’s old payroll tax rate of 1.5%, which San Francisco voters reduced in favor of a gross receipts tax in 2011.

The proposal comes shortly after two major tech companies, Lyft and Pinterest, made their Wall Street debuts. Uber is expected to thunder into the public market this year with its reported $100 billion valuation.

While some worried that levying another business tax could push jobs out of the city, others considered the proposal a fair price for wealthy San Francisco companies to pay.

“We have a big tax burden compared to nearby jurisdictions, which any of these companies could relocate to if they wanted to lower their tax bill,” San Francisco Chief Economist Ted Egan said.

Jim Wunderman, CEO of the Bay Area Council, said he thought the tax was a “terrible idea” that would discourage future startups and jobs in the city.

“I think there is a deep lack of understanding of what is brought to the city and the Bay Area by having this incredible cluster of innovation and knowledge in San Francisco,” he said.

Mar plans to propose the measure to the Board of Supervisors sometime in May. Six of his colleagues would need to support it to place it on the ballot. Then it would need a two-thirds approval from the voters to pass in November.

Preliminary city estimates show that the tax could collect between $100 million and $200 million in the first two years, possibly more, Mar said. The proceeds would be dedicated to programs that address income inequality, such as those that support workforce development, small businesses and affordable housing.

So far, 2019 is on track to be the biggest year for initial public offerings in recent history, as companies such as Slack, Airbnb, Cloudflare and Postmates also plan to enter the public market. The influx of wealth will likely have a direct impact on the city’s housing market, Egan said.

Egan estimates that the Lyft and Pinterest IPOs and Uber’s upcoming entry could lead to a 0.5% to 1.9% increase in the city’s already sky-high housing prices. He said the current median monthly rent of $4,400 may increase by a range of $24 to $81, while the median home price of $1.3 million may increase by between $7,000 to $25,000.

Mar held a hearing Wednesday to discuss the impact of the looming “IPO earthquake” on the city.

At the hearing, several public commenters — from community advocates to workers rights groups and ride-share drivers — spoke of how difficult it is to make ends meet in pricey San Francisco, and urged the city to do something to narrow the gap between the rich and the poor.

“I have to live with six other people in a two-bedroom apartment,” Mostafa Maklad, a San Francisco resident and Uber driver, said. “Uber executives and employees are set to become millionaires and gain more wealth, and will dodge the responsibility to the workers in the city.”

Kung Feng, executive director of Jobs with Justice, said he sees the IPO tax as a “restoration of something we lost” when the city granted a tax break to certain companies that moved into Mid-Market several years ago. That tax break is set to expire this month.

“I think it’s time to turn the city around, and this is a good first step in that,” Feng said of the tax proposal. “Instead of leading the country in income inequality, we should be leading the country in equality.”

Mar’s tax would be retroactive to the date of introduction, which means it would capture all companies that go public from May onward. The companies would be subject to the tax when their employees cash out their stock options, which means Lyft and Pinterest could still be impacted by the measure.

If the supervisors agree with Mar, it would highlight the contrast with the city’s situation of just eight years ago, when it was crawling out of the Great Recession. In 2011, legislators scrambled to lower the city’s unpopular payroll tax — which included stock-based options — so companies would stay in the city.

Supervisor Rafael Mandelman said Wednesday that he still needs to review the proposal but would be open to taxing stock-based compensation.

“It’s great that they’re here, but we have to make sure they’re giving back a fair share for public needs,” he said of tech companies.

But Supervisor Catherine Stefani said, “It’s arrogant to think they won’t leave if we tax them.”

“We need to be very careful ... that we don’t tax in a way that will hurt our economic prosperity,” said Stefani, who said she also needs to review the official language before taking a firm stance on the tax.

Meanwhile, Mar said he is not concerned about how his proposal could push companies out of the city.

“The tech sector is very much ingrained in San Francisco and in our economy and culture,” he said. “And I don’t really see them leaving.”

Trisha Thadani is a San Francisco Chronicle staff writer. Email: tthadani@sfchronicle.com Twitter: @TrishaThadani