NEW YORK (Reuters) – In a decision that may slow foreclosures nationwide, Massachusetts' highest court voided the seizure of two homes by Wells Fargo & Co and US Bancorp after the banks failed to show they held the mortgages at the time they foreclosed.

Bank shares fell, weighing on broader stock indexes, on fears the decision could threaten lenders' ability to work through hundreds of thousands of pending foreclosures.

The Supreme Judicial Court of Massachusetts' unanimous decision on Friday upheld a lower court ruling. It is among the earliest cases to address the validity of foreclosures done without proper documentation.

That issue, including the use of "robo-signers" who approved foreclosure documents without reviewing them, last year prompted an uproar that led lenders such as Bank of America Corp, JPMorgan Chase & Co and Ally Financial Inc to temporarily stop seizing homes.

"A ruling like this will slow down the foreclosure process" for lenders, said Marty Mosby, an analyst at Guggenheim Securities in Memphis, Tennessee. "They're going to have to be really precise and get everything in order. It doesn't leave a lot of wiggle room."

Wells Fargo and U.S. Bancorp lacked authority to foreclose after having "failed to make the required showing that they were the holders of the mortgages at the time of foreclosure," Justice Ralph Gants wrote for the Massachusetts court.

In a concurring opinion, Justice Robert Cordy lambasted "the utter carelessness" that the banks demonstrated in documenting their right to own the properties.

Courts in other U.S. states are considering similar cases, and all 50 state attorneys general are examining whether lenders are forcing people out of their homes improperly.

Friday's decision applies in Massachusetts, and need not be followed by federal judges or by courts in other states.

Nonetheless, "it will be certainly cited as persuasive authority by anybody in a similar scenario who's trying to hold onto his home," said Robert Nislick, a real estate lawyer at Marcus, Errico, Emmer & Brooks PC in Braintree, Massachusetts.

LEAVING PAPERWORK BEHIND

Analysts said the decision may also raise the specter that loans transferred improperly will need to be bought back.

"What they were doing was peddling these mortgages and leaving the paperwork behind," said Michael Pill, areal estate partner at Green, Miles, Lipton & Fitz-Gibbon LLP in Northampton, Massachusetts who is not involved in the case.

The Massachusetts court rejected a request by the banks to apply the decision only in future cases, leaving homeowners already foreclosed upon without a remedy. Gants chided the banks for ignoring settled rules in their "rush" to sell mortgage-backed securities.

A spokeswoman for San Francisco-based Wells Fargo, Teri Schrettenbrunner, had no immediate comment on the decision.

U.S. Bancorp spokesman Steve Dale said the decision has no financial impact on the Minneapolis-based bank, which has "no responsibility" for the terms or means of transfer of mortgages used in the securitization trusts it oversees as trustee.

Martha Coakley, Massachusetts' attorney general, praised Friday's decision. "In their careless and hasty stampede to securitize loans, the banks moved at their own peril," she said. "They should bear the brunt and the cost of the remedy."

In Friday trading, Wells Fargo shares closed down 65 cents, or 2 percent lower, at $31.50, while U.S. Bancorp shares fell 20 cents, or 0.8 percent, at $26.09.

Bank of America stock fell 1.3 percent and JPMorgan fell 1.9 percent, and the KBW Bank Index fell 0.9 percent. Broader share indexes declined about 0.2 percent.

Bank shares recovered some losses after it was revealed that Maine's highest court on Thursday allowed JPMorgan to conduct a foreclosure proceeding despite not having possessed the underlying mortgage until after that process began.

NOT IMMUNE

In the Massachusetts case, U.S. Bancorp and Wells Fargo had said they controlled through different trusts the respective mortgages of Antonio Ibanez and the married couple Mark and Tammy LaRace, who lost their homes to foreclosure in 2007.

The banks bought the Springfield, Massachusetts, homes in foreclosure, and sought court orders confirming they had title. A lower court judge ruled against them in March 2009.

"It is the first time the supreme court of a state has looked straight at securitization practices and told the industry, you are not immune from state statutes and homeowner protections," Paul Collier, a lawyer for Ibanez, said in an interview.

Massachusetts is one of 27 U.S. states that do not require court approval to foreclose.

"I'm ecstatic," Glenn Russell, a lawyer for the LaRaces, said in an interview. "The fact the decision applies retroactively could mean thousands of homeowners can seek recovery for homes wrongfully foreclosed upon."

Russell said the LaRaces moved back to their home after the 2009 ruling, while Collier said Ibanez has not. "U.S. Bancorp will have to compensate him in exchange for the deed, or will have to walk away," Collier said.

Analysts said the decision could make it harder to sell homes, and perhaps weigh on the nation's economic recovery.

"The inventory on foreclosures will keep a lid on housing prices for some time," said Blake Howells, head of equity research at Becker Capital Management in Portland, Oregon.

Gants did suggest in his opinion how banks might properly transfer mortgages via securitization trusts.

"The executed agreement that assigns the pool of mortgages, with a schedule of the pooled mortgage loans that clearly and specifically identifies the mortgage at issue as among those assigned, may suffice to establish the trustee as the mortgage holder," Gants wrote. "However, there must be proof that the assignment was made by a party that itself held the mortgage."

The American Securitization Forum, a trade group, in a statement said it "is confident securitization transfers are valid and fully enforceable."

The cases are U.S. Bank N.A. v. Ibanez and Wells Fargo Bank NA v. LaRace et al, Supreme Judicial Court of Massachusetts, No. SJC-10694.