Goldman Sachs and Morgan Stanley are believed to be among eight US banks facing an investigation into the rating of their mortgage products.
It is believed New York Attorney General Andrew Cuomo is looking at whether the relationship between the banks and credit rating agencies was manipulated to gain a better ratings for risky securities, the BBC reports.
He has requested information from the eight banks, as well as the three major rating agencies - Standard and Poor's, Moody's and Fitch Ratings.
Bad US mortgage debt was one of the main causes of the financial crisis as much of the investments were repackaged into wider debt offerings and then resold around the world.
Last month, the SEC charged Goldman Sachs with civil fraud over the way it marketed its subprime mortgage products prior to the crisis.
The US senate recently voted in favour of tougher regulation of the credit rating agencies.
Under the proposals, US regulators will be in charge of deciding which rating agencies should rate products from different banks.
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