Of all the proposed solutions to the state’s soaring housing costs, one has caused perhaps the most anxiety, anger and passion — rent control.

In November, it’s back again. This time, it’s on the ballot as Proposition 21, a broad extension of rent control laws which could dramatically increase the number of price-controlled units in the state.

California already enacted new price caps and eviction protections on January 1, but high housing costs and the punishing economic downturn during the COVID-19 pandemic have heightened tensions between landlords and tenants.

Proposition 21 would allow municipalities to enact rent control on homes built at least 15 years ago, with units added every year as they age out of the exemption. It would not cover small landlords who own a maximum of two homes, although opponents say that protection is limited. It’s the second statewide rent control referendum, following Proposition 10 which was roundly defeated in 2018 and also brought by the AIDS Healthcare Foundation.

Real estate groups say rent control will make the housing crisis worse, discouraging investors from building new apartments, while favoring existing tenants regardless of income and pushing up costs on newcomers.

Proponents say the housing and homelessness crisis has deepened in the past two years. The economic pain and widespread unemployment caused by the pandemic has punished workers already struggling to afford a place to live.

“It made this terrible housing crisis much, much worse,” said René Moya, campaign director for the Yes on 21 effort. “The world has changed, and not for the better.”

Tenant advocates point to a punishing trend for many workers: median wages in California have risen about 10 percent since 2000, while the median rent has grown 35 percent.

Edie Keating of Mountain View Housing Justice Coalition said the referendum would help tenants in fast-growing cities in Silicon Valley. Although several Bay Area cities already have rent ordinances, cities need additional tools to create greater housing security, especially for newer residents, she said.

In San Jose, she said, “it would make a huge difference.”

The referendum is opposed by a variety of real estate and landlord groups. They point to studies by think tanks and Stanford economists finding similar rent control laws reduce available middle class and affordable housing, and drive up rents for residents not covered by the law.

“In the long run, it results in a housing freeze,” said Steven Maviglio of the Californians for Responsible Housing campaign.

San Jose landlord and real estate agent Gustavo Gonzalez said the measure would burden small property owners with another set of rent control laws. Gonzalez owns two small, older buildings downtown, and said he keeps rents low to minimize turnover in his units.

But with additional administrative costs and the prospect of lower future income, he said he could be forced to raise rents. “We need more housing,” he said. “This will kill housing development.”

Tension between landlords and tenant groups has grown. Bay Area tenants have held regular demonstrations, including a group of squatters taking over an Oakland house. San Francisco, San Jose and Oakland are among the priciest cities in the nation to rent, but landlords say they have their own soaring costs.

Roughly 45 percent of California’s population — 17 million people — live in rented homes and apartments. In the Bay Area, San Francisco has the highest portion of renter households in the region, with 62 percent, followed by Oakland (60 percent) and San Jose (43 percent).

San Jose’s rent ordinance covers most units occupied before September 1979. The city estimates 38,000 apartments are under rent control, with single-family homes, condos and duplexes exempt. In Oakland, rent control covers most apartment units built before 1983, and Hayward has price controls on most units built before July 1979.

A defeat of the measure would preserve the status quo, leaving rent control up to cities under the boundaries of the state’s 1995 Costa-Hawkins law. That measure bans cities from placing rent caps on units built after February 1995, and exempts single-family homes and condos from controls. It also prohibits price caps from being carried forward when a new renter moves into a unit, known as vacancy control.

A study by the state Legislative Analyst’s Office found Proposition 21 would increase local government costs to set up a system to regulate rents, decrease property values for apartment complexes, and result in less property tax collection on rentals. Tenants would likely move less often and pay more sales taxes with their increased discretionary income.

The campaign is expected to be high-priced and contentious.

Gov. Gavin Newsom opposes Prop 21. Assemblymember David Chiu, D-San Francisco, chairman of the housing and community development committee, has endorsed it. Chiu authored AB 1482 last year, the latest reform to state rent control. That law went into effect this year and limits rent increases on most older apartments to a maximum of 10 percent annually, and restricts some evictions.

Proposition 21 was placed on the ballot by the AIDS Healthcare Foundation and its controversial president, Michael Weinstein. Earlier this year, housing advocates filed a formal complaint with the state charging the foundation improperly spent hundreds of thousands of dollars to kill a pro-housing production bill. Weinstein said at the time the bill would have encouraged gentrification.

The health care foundation in 2018 backed a similar rent control measure, Proposition 10, and saw it defeated statewide by 20 points. The foundation led a consortium to raise $24.5 million on the last campaign.

The opposition effort is backed by the California Apartment Association, which led a coalition that raised $53 million to defeat the 2018 proposition.

In this year’s campaign, supporters have raised nearly $23 million so far, while opponents have raised $48 million.