The lawsuit was filed on behalf of Bear Stearns clients who invested in mortgage bonds sold by two Bear Stearns hedge funds.
The bonds were highly rated by Moody's Investors Service, Standard & Poor's or Fitch Ratings just before the financial crisis of 2008.
Bear Stearns collapsed in 2007 -- one of the early victims of the financial crisis.
The New York Times reported Monday that lawyers have filed a 141-page complaint that includes a significant number of emails that indicate the rating services knew they were proving high ratings for risky bonds simply because there were lucrative fees involved.
"We sold our soul to the devil for revenue," one email written by a Moody's employee says.
One written by an S&P employee calls the rating system a "scam." Another, dating in 2007, from an S&P employee says, "It could be structured by cows and we would rate it."
The Times said that the two managers of the funds, Ralph Cioffi and Matthew Tanin, were found not guilty of fraud in a civil case. In a second case, Cioffi and Tanin both settled allegations from regulators without admitting any wrongdoing.