San Francisco’s skyline is growing, and the economy is booming as developers prepare to build another wave of office projects.

But a powerful, longtime South of Market activist wants to hit the brakes, and he’s asking voters to help.

The March primary election will include Proposition E, sponsored by activist John Elberling and his nonprofit, Todco.

If passed, Prop. E would reduce the amount of office space the city can approve each year by a percentage equal to the city’s affordable housing shortfall. That shortfall is based on a state-mandated goal of building at least 2,042 homes per year. The measure would almost certainly cut office growth, because the city has built an average of 712 affordable units a year in the past decade.

Prop. E would further tighten Proposition M, a 1986 voter-approved law that limits the city to approving no more than 875,000 square feet of large office projects each year. If the city approves less, the unused square footage rolls over to future years.

“The commercial sector is growing so fast because of the boom,” said Elberling, executive director of Todco. “We’re not keeping up with the transportation. Everybody knows that’s true. And we’re not keeping up with the housing needs of all the new workers that are flooding into the Bay Area.”

“Any rational person, I would think, says, ‘Oh, then we should slow down until we can until we can catch up,’” he said.

But critics say the measure would do great harm to the economy and exacerbate the city’s housing crisis, pushing growth to the South Bay and Oakland, while cutting office fees for affordable housing in San Francisco. Opponents also argue it will drive up office rents, forcing out nonprofits and small businesses that can’t afford pricey office space.

Prop. E would cut $600 million to $900 million in affordable housing fees and reduce property taxes by $1 billion to $1.5 billion by 2040, according to the city’s Office of Economic and Workforce Development.

A study by the city’s chief economist said that if the measure passes, disposable personal income will drop 5.9% by 2040, and the city will have 7.9% or 91,000 fewer jobs.

Opponents include the San Francisco Chamber of Commerce and San Francisco Building and Construction Trades Council, which represents union workers. SPUR, a regional planning think tank whose members include developers, also opposes the measure.

“The effect of this ballot measure will be to shift offices out of the city, but leave the housing crisis with us. But we will no longer have any of the revenue to address it,” said Jay Cheng, the chamber’s public policy director. “The end result of Prop. E will literally take money out of people’s pockets. It’s really a no-win scenario.”

SPUR noted that the measure doesn’t create any new funding for housing.

“Prop. E definitely promises one thing but is actually going to reduce affordable housing funding,” said Nick Josefowitz, director of policy at SPUR. “Prop. E does nothing to make it easier to build affordable housing.”

Josefowitz said streamlining affordable housing approvals and raising more money for below-market units is a better approach.

Mayor London Breed also opposes the measure and had previously sponsored a competing proposal that would have lifted some office restrictions. She pulled her measure to focus on other issues such as homelessness, her spokesman previously said.

Under Prop. E, office projects that provide affordable housing and below-market-rate community and retail space could win approvals sooner, as an incentive to provide more benefits. But Cheng said that wouldn’t affect a significant number of projects.

Opponents face an uphill financial battle. Campaign finance disclosures show the Yes on E campaign has raised $407,353 to date, while opponent have raised $32,500. Cheng said additional commitments bring the opponents’ total support up to around $60,000.

Todco, which owns 956 affordable housing units in the South of Market, previously refinanced the buildings to raise millions of dollars that it’s deployed for ballot measures it supports.

Meanwhile, the city’s largest office developers have stayed out of the fight.

Prop. M’s existing office limitations have become a major obstacle for office developers in the newly rezoned Central SoMa district, because the number of office projects chasing approvals exceeds the bank, which is nearly exhausted. Prop. E would help those projects by accelerating approvals of up to 1.7 million square feet for six large office projects, including redevelopment of the San Francisco Flower Mart and 88 Bluxome, which would replace a tennis club. Some of those projects have received approvals for their first phase of development, but not their second.

As a result, those developers, which include some of the city’s largest property owners and developers, such as Boston Properties and Kilroy Realty, haven’t contributed to oppose Prop. E, Cheng said.

On recent corporate earnings calls, some real estate executives said Prop. E could benefit existing landlords by limiting supply and putting more pressure on office rents, which are already at record highs.

“We’re not hearing anything from any tenants as far as it’s impacting their desire to be in San Francisco or they’re looking elsewhere. And San Francisco has always been a difficult market to develop in. So I don’t think it really changes anything,” Robert Pester, executive vice president of the San Francisco region at Boston Properties, said on the call. “What the impact will be is (for) existing product, the rent should continue to rise substantially because it’s going to restrict supply.

Rob Paratte, Kilroy executive vice president of leasing and business development, declined to comment on the merits of the measure on an earnings call, but said it would probably make it harder for large office projects to move forward.

“It’s going to bode well for rental rates and asking rates because it’s just going to make San Francisco tougher to develop in,” he said.

Only one developer, Oz Erickson of the Emerald Fund, which builds housing and not offices, has donated to oppose Prop. E.

“Restricting office supply will simply raise office rents in the city and will negatively affect struggling nonprofits whose work is so important to the well-being of San Francisco. What happens to the food banks, the homeless care providers, the domestic violence responders when their rents suddenly increase due to restricted office supply? They will be forced out of the city, and the city will be worse off,” Erickson said.

Doug Engmann, the co-chairman of the original Prop. M campaign, said he strongly supports Prop. E and that new offices don’t pay enough to offset their strain on housing and transit.

“We’ve had too much growth, particularly office growth, outstripping our infrastructure and affordable housing,” Engmann said.

Shifting some office growth to nearby cities will help reduce housing demand, even if the San Francisco loses out on fees, he said.

Elberling said a solution to regional disparities is to widen office restrictions.

“What we think is that every city needs a Prop. E,” Elberling said. “Long term, every county, every city should balance growth, jobs and housing.”

Roland Li is a San Francisco Chronicle staff writer. Email: roland.li@sfchronicle.com Twitter: @rolandlisf