Federal prosecutors have decided not to bring criminal charges against Chicago law firm Sidley Austin over its involvement with illegal tax shelters, though the law firm will pay a civil penalty of $39.4 million to the Internal Revenue Service.

In announcing the decision Wednesday, U.S. Attorney Michael J. Garcia of the Southern District of New York distinguished the actions of the firm from that of former tax partner Raymond J. Ruble, who is already facing a criminal trial in Manhattan federal court.