The U.S. Justice Department is suing Standard & Poor's Ratings Service, accusing the financial services company of helping to cause the mortgage crisis.

They allege S&P willfully tried to defraud investors with inaccurate ratings on the mortgage bonds that were loaded with risky subprime mortgages.

"The DOJ is playing hardball and they're coming at the ratings agency in a very different direction with a potentially very powerful weapon to push S&P to the settlement table," Jeffrey Manns, a law professor at George Washington University, told the Los Angeles Times.

The Wall Street Journal reports the S&P is defending their ratings, saying they were issued in good faith.