New York Attorney General Eric Schneiderman is examining the nation's biggest credit rating agencies' compliance with agreements reached in 2008.

The agreements imposed no financial penalties but required Moody's Investors Service, Standard & Poor's and Fitch Inc. to publicly disclose due diligence and evaluation criteria.

They also required partial upfront payments to prevent banks from simply buying the better ratings for those securities.

With that market already collapsed, the agencies weren't rating new mortgage-backed securities. The 42-month agreements expired in 2012.

An official with knowledge of the investigation who was not authorized to speak publicly says a subpoena this week went to S&P and information requests to Moody's and Fitch.

The U.S. Justice Department separately sued S&P over mortgage bond ratings.