Facebook Inc. (FB) - Get Report shares traded lower Thursday amid reports that the U.S. Department of Justice will launch yet another antitrust probe into the world's largest social media network.

Reuters reported late Wednesday that the DoJ is ready to investigate the group, but did not reveal under which specific grounds the probe would be based. Bloomberg reported the DoJ was moved to look into Facebook by U.S. Attorney General William Barr, who appears to have overridden an earlier agreement with the FTC to split their probes into U.S. tech giants, including Apple Inc. (AAPL) - Get Report , Amazon Inc. (AMZN) - Get Report and Google (GOOGL) - Get Report , by targeting separate companies. 

Facebook is currently the subject of at least three separate investigations, including an antitrust probe lead by the Federal Trade Commission and broader scrutiny from two groups of state attorneys general announced earlier this month. 

Facebook shares were marked 1.5% lower at the start of trading Thursday to change hands at $180.04 each, a move that would trim the stock's six month gain to around 8%.

Earlier this year, Facebook settled a previous dispute with the FTC, and paid a $5 billion fine over its handing of data linked to the Cambridge Analytica scandal.

The FTC's probe had centered around whether Facebook violated a 2012 consent decree mandating that the social network better protect users' personal information.

Facebook tallied $55.8 billion in annual revenues last year, and set aside $3 billion for the expected penalty prior to its agreement, giving it more than enough room to absorb what was the biggest fine ever paid by a public company to the FTC.

Democrat lawmaker David Cicilline, who chairs as House antitrust panel, called the fine "a Christmas present five months early" that "won't make them think twice about their responsibility to protect user data."