The letter, from a real-estate company representing a bank, said his building was in foreclosure and he had to "vacate the premises."

The company offered Mr. Carreiro and the other residents of the three-unit building, including the landlord, a payment to help with moving expenses if they left within 30 days. But he says the firm wouldn't disclose the size of the payment unless he agreed to leave.

Mr. Carreiro rejected the offer, saying he had nowhere else to go. Now he has to appear in court next month for an eviction hearing. "It's very frustrating, because I was making my [monthly] payments but now I get evicted," said Mr. Carreiro, who is disabled and unemployed, and gets rental assistance from the government. "I can't afford to leave."

Mr. Carreiro's case isn't unique. As U.S. foreclosures soar, renters -- especially in small apartment buildings and single-family homes -- are paying a high price for their landlords' financial troubles. Across the U.S., thousands of people are being evicted.

Renters are particularly vulnerable now for a couple of reasons. As lending standards were relaxed in recent years, more people snapped up properties that they rented out, or partly rented out. When they couldn't make their mortgage payments -- sometimes because their adjustable-rate mortgages reset to higher rates -- the properties ended up in foreclosure. In most places in the U.S., that voids tenants' leases.

Unlike larger apartment buildings owned by commercial enterprises, homes and small multifamily properties typically aren't run by management companies. Banks, which aren't equipped to handle utility and water bills, maintenance and insurance requirements, want to sell foreclosed property as soon as possible, and often that means getting rid of the tenants.

Industry officials say it is easier to sell empty properties -- especially if a prospective buyer is interested in moving in right away. "You have to remove the tenant[s], or the property value spirals downward," said Vicki Vidal, senior director for government affairs at the Mortgage Bankers Association.

Renters in large apartment buildings don't face the same pressure to leave those properties, which are usually owned and operated by real-estate companies. Even if the buildings go into foreclosure, the potential buyers want a building with lots of tenants and a steady monthly income.

However, renters of condominiums are vulnerable to foreclosures. Condos often are owned by individuals who use mortgages to buy them. If the owner defaults on his mortgage, his renter may face eviction.

Often, the small multifamily dwellings entering foreclosure are in older urban neighborhoods with a lower-income population. That's the same demographic, critics say, that was targeted by predatory lenders peddling mortgages with introductory "teaser" rates that reset to higher rates.

"The biggest problem in this industry is that you could buy a three- or four-family home with no money down," said Anthony Rondeau, a vice president of Select Financial Mortgage Corp. in East Providence, R.I. "[Mortgage] brokers were shoving this through the system -- it didn't matter that I didn't do it, because someone else would."

For many renters, finding an affordable apartment can mean a long, difficult search, and moving costs can be a financial blow.

Delecia Mitchell, 24, lives on the bottom floor of a Chicago "two-flat," or two-family home, with her three sons. Last month, she found an eviction notice tacked to the door. Her landlord, who lives upstairs, had defaulted on the mortgage. Ms. Mitchell, who is six months pregnant, dreaded the idea of moving. She said finding an affordable apartment would take at least two or three months.

Renters' protections vary, depending on state and locality. In many cases, tenants get just 30 days' notice. Now, some tenants' advocates and lawmakers are pushing for beefed-up protections. New legislation in Illinois, which takes effect in January, will require that tenants get 120 days' notice. And the U.S. House of Representatives recently passed legislation that would require new owners to honor leases of tenants for as long as six months after foreclosure.

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