We’ve been following the Google Book Search Settlement closely. Today, PCWorld reports that the U.S. Department of Justice has confirmed that it is investigating possible antitrust violations by the Google Book Search settlement.

In a filing to the judge overseeing the settlement of a lawsuit filed by The Authors Guild against Google, the DOJ informed the court that it has opened an investigation into the proposed settlement after reviewing public comments of concern. Those comments suggest that the agreement might violate the Sherman Act, a U.S. antitrust law, the DOJ said.

“The United States has reached no conclusions as to the merit of those concerns or more broadly what impact this settlement may have on competition. However, we have determined that the issues raised by the proposed settlement warrant further inquiry,” the letter reads.

It also says the DOJ has already demanded access to documents and other information from parties in the litigation and expects to have ongoing discussions with them as well.

There’s a hearing with Judge Denny Chin scheduled for Oct. 7, which is a full month after the September 4th deadline to make a choice about opting in or out.