A coalition of as many as 40 state attorneys general is expected Wednesday to announce an investigation into the mortgage-servicing industry, an effort some of them hope will pressure financial institutions to rewrite large numbers of troubled loans.

The move comes amid recent allegations that mortgage-servicers, which include units of major banks such as Bank of America Corp., submitted fraudulent documents in thousands of foreclosure proceedings nationwide.

The banks say the document problems are technical—largely the result of papers approved by so-called robo-signers with little review—and don't reflect substantive problems with foreclosures. Still, they have drawn criticism from consumer advocates and state and federal lawmakers.

"I think the mortgage-servicing firms need to understand that they face real exposure now, and they would be well advised to take this very seriously, to clean this up by doing loan workouts to keep people in their homes, which up till now they've just paid lip-service to," said Ohio Attorney General Richard Cordray.

Some in Congress have called for a moratorium on all foreclosures until the documentation issue is resolved, though senior Administration officials Monday again declined to endorse that idea. Servicers that have lied to courts by filing incorrect paperwork "need to suffer the consequences for their irresponsible actions," said Shaun Donovan, the Secretary of the U.S. Department of Housing and Urban Development. But "where we have not found problems with particular servicers…we do have some risk of going too far."

The attorneys' general immediate aim is to determine the scale of the document problems and correct them. But several of them have said that the investigation could force the lenders and servicers to agree to mass loan modifications or principal forgiveness schemes. Other possibilities include financial penalties or changes in mortgage servicing practices.

Lenders and servicers have largely resisted reducing principal on mortgages, instead focusing on interest-rate reductions or term extensions. Banks say they are worried about lawsuits from investors, some of whom could lose money in a principal write down.

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