Standard & Poor’s said it expects to be the target of a U.S. Department of Justice civil lawsuit over its mortgage bond ratings, the first federal enforcement action against a credit rating agency over alleged illegal behavior tied to the recent financial crisis. …

It is unclear why regulators may be now focusing on S&P rather than Moody’s or Fimalac SA’s Fitch Ratings.

S&P, Moody’s and Fitch have long faced criticism from investors, politicians and regulators for assigning high ratings to thousands of subprime and other mortgage securities that quickly turned sour.

“This lawsuit is significant because it could augur future government action or, even worse for the agencies, more litigation by investors,” said Jeffrey Manns, a law professor at George Washington University in Washington, D.C. …

The New York Times reported that talks between the Justice Department and S&P broke down last week after the government sought a settlement of more than $1 billion.