The US Justice Department will open an antitrust investigation of Facebook, a source familiar with the matter said on Wednesday.

It will mark the fourth recent investigation of the social-media company, which also faces investigations by the Federal Trade Commission, a group of state attorneys general led by New York, and the House of Representatives Judiciary Committee.

Reuters and others reported in June that the agencies had divided up the companies being investigated, with the Justice Department taking Alphabet's Google as well as Apple, while the FTC looked at Facebook and Amazon.

The Justice Department later said it was opening an investigation of online platforms without saying which ones. This led some industry observers to question whether the two federal investigations would overlap.

Lawmakers, in particular Sen. Mike Lee, the chair of the Senate Judiciary Committee's antitrust panel, criticized the appearance of an overlap in a hearing last week.

The agencies generally have a practice of meeting to decide who will investigate which matter, but the FTC cannot investigate certain matters, for example price-fixing.