(08-14) 21:38 PDT -- In early June, a handwritten note appeared on the front door of Bing Ling Zeng's San Francisco apartment, written in a language she couldn't understand.

"You will be needing to vacate this property soon," it said.

The following month, Pacific Gas and Electric Co. shut off the power. The food in the refrigerator spoiled, forcing Zeng to go out several times a day to buy groceries and milk for her three young children. Her 62-year-old mother-in-law couldn't recharge her electric wheelchair.

Zeng and the other Chinese family sharing the space hadn't fallen behind in their rent or bills. The only thing they did wrong was to lease an apartment from a landlord who fell into foreclosure, an unforeseeable mistake that hundreds are grappling with across San Francisco.

Tenants' groups around the city report a sharp rise in such cases, as lenders repossess growing numbers of local homes. Renters are being told to leave, are living in the dark or are receiving little response to their complaints as their homes fall into disrepair.

State and local laws prohibit landlords from evicting tenants or shutting off utilities in most circumstances like these, but not all renters are aware of the rules, and not all of the entities that take control of properties try to learn them.

"The basic problem is that the people who are acquiring these properties, they don't understand or want to understand that tenants have rights in San Francisco," said Tommi Avicolli Mecca, director of counseling programs at the Housing Rights Committee of San Francisco. "You can't just go in and tell them to leave, you can't shut off utilities, you can't call the police, you can't do any of that stuff."

He and other tenant advocates and attorneys worry that many renters who aren't aware of these rules are being pressured into handing over their keys.

The issue was virtually unheard of a year ago. The San Francisco Tenants Union had to circulate a memo to its counselors earlier this year because few had ever encountered it before.

The exact number of tenants dealing with the aftermath of a landlord foreclosure is difficult to ascertain. Three tenants groups contacted by The Chronicle reported around 130 cases this year, but most counselors believe that many more tenants aren't contacting the organizations. What is known is that lenders foreclosed on 492 homes in San Francisco during the last year and a half, according to DataQuick Information Systems.

One of those properties was on London Street, in the Excelsior district, where Daniela Medrano has lived with her daughter since 2005. Shortly after the lender repossessed the home in December, an agent with Manhattan Realty Group of South San Francisco, hired to sell the building, told Medrano she had to leave within 30 days, Medrano says.

After she refused, the agent threatened to call the police or sheriff's department, and have them forcibly removed on at least two occasions, Medrano alleges.

Medrano was "completely frustrated," she said through a translator. "I didn't know where to go or who to go to."

Sunny Bali, the owner of Manhattan Realty, said in a prepared statement that the company did approach the tenants and offered relocation expenses if they would leave voluntarily. He denied that any threats were made or notices of eviction issued. He said the tenants became uncooperative after they were asked to leave temporarily so that multiple building code violations, for which the bank was being fined, could be fixed.

"We are aware that they have approached many organizations and agencies and have tried to portray Manhattan Realty Group as this evil company," he said. "Far from true. We have done every thing correctly and diligently, as we always try to do."

Lenders who take back properties or investors who pick up foreclosed homes generally prefer the buildings empty, because that makes them easier to sell. Under San Francisco laws, however, those aren't grounds for an eviction in a rent-controlled building.

Unless tenants have stopped paying rent or otherwise have misbehaved, generally they can be forced out only when a new owner plans to demolish the property, has secured the necessary approvals to convert into it condominiums or plans to move in family members or him or herself, according to the city's rent ordinance. Even then, the owner typically must provide several months' notice and thousands of dollars in relocation costs.

In addition, new owners - a bank, a trustee or otherwise - generally become liable for the same obligations of the previous landlord, said Robert Collins, deputy director of the San Francisco Rent Board. That means that if the original lease said the landlord pays for electricity, as Zeng said was the case for her Excelsior apartment, the company that bought it is responsible now.

Nevertheless, the Zengs' power stayed off for a week. It was switched back on only after the Housing Rights Committee contacted PG&E and tracked down New Vista Asset Management, which took control of the Huron Avenue property, Avicolli Mecca said.

The note left on the door, stating that the families "would be needing to leave soon," was from a real estate agent representing New Vista.

"I left that for them because I knew the bank's ultimate wish is for them to be kicked out," said Frances Medina of Century 22 Real Estate and Mortgage. She stressed that she was "in no way involved in the eviction process."

New Vista of San Diego didn't respond to inquires from The Chronicle.

PG&E spokesman Joe Molica said the utility has a policy to help customers in this situation. Among other things, it posts notices at homes letting tenants know that they can assume utility payments without become liable for the landlord's previous bills, and can deduct that amount from their monthly rent.

"We're more than willing to help our customers who are in difficult situations with their landlords," Molica said.

Even if the law is largely on the tenants' side in these circumstances, relaying the rights of tenants and responsibilities of landlords is a challenge, said Ken Greenstein, partner at San Francisco tenant law firm Greenstein and McDonald.

In an era when mortgages are bundled and sold to investors, just figuring out who owns a property after a foreclosure - and is responsible for duties described in a lease signed years ago - can be difficult. Since investors buying homes often say, in financial documents, that they will live in the homes, , when in fact they plan to rent the properties, it can be hard for the city, new owners or PG&E to know which homes actually are occupied by tenants. And the neighborhoods hardest hit by foreclosures are also areas with large immigrant populations, where language barriers and issues of legal status form yet another impediment.

To help bridge the communication gap, the city will soon begin sending letters in multiple languages to tenants in repossessed homes, advising the occupants to contact the Rent Board and housing counseling agencies, Assessor-Recorder Phil Ting said. Similarly, Supervisor Tom Ammiano has asked PG&E to find ways of ensuring occupied apartments aren't unplugged after a foreclosure.

In an e-mail, Ammiano said electricity is a basic necessity that all tenants should be able to depend on.

"There has been a lot of talk about the impact of the housing crisis on property owners, however, tenants are the underreported victims," he said. "Unlike homeowners, who know that their home is at risk, renters have no warning before the power is turned off or someone is at the door telling them they need to pack up and move by the next day."

If a renter is harassed into leaving an apartment, or if he or she vacates without receiving the proper amount of notice or relocation money due under local regulations, that person could have a case to sue, Greenstein said. Likewise, when a new owner doesn't pay for or shuts off utilities, the tenant could have grounds to sue under the state civil code, he said.

But tenant protections do have their limits. While Zeng and her family probably can't be evicted by the current owner, she remains worried about what will happen when the building is sold again, as Medina says the company intends to do. The new owners may want to move in, which probably would allow them to begin legitimate eviction proceedings.

"It will be very difficult to find a place we can afford in San Francisco," Zeng said through a translator, adding that rents have increased and landlords often don't want to lease to families with children. "We're very scared that we won't be able to find a new place to live. It makes me very sad."

E-mail James Temple at jtemple@sfchronicle.com.