The Justice Department said Saturday it is investigating five major TV networks over their brief boycott of White House pool coverage.

ABC, CBS, CNN, NBC and Fox News make up the TV press pool. It records the president's daily events and shares the video with other outlets. The networks were told to hand over "communications and materials" about the pool, the Washington Examiner reported, citing The New York Times, which first reported the probe.

"Members of the television press pool have boycotted covering White House events," department spokesperson Emily Covington said. "Group boycotts among commercial competitors can violate the Sherman Act. The Antitrust Division is simply investigating to determine whether these news organizations have violated the antitrust laws."

The fight began Sept. 18. The White House pulled the credentials of reporters from CNN, MS Now and Politico. It cited what President Donald Trump called "FAKE NEWS" and national security concerns about their Iran war coverage. In response, the five networks paused pool coverage for several days. That included the start of Trump's summit with Chinese President Xi Jinping.

The three outlets sued, arguing the ban violated the First Amendment. A judge ruled for them, and the White House restored their access, the BBC reported.

It was not clear how the department sees the pause as an antitrust violation, CBS News reported. The Sherman Act targets monopolies and unfair business practices. The networks did not immediately comment. Al Jazeera said the probe adds legal and financial pressure on the media to keep covering the president.

What we know: The Justice Department is investigating whether ABC, CBS, CNN, NBC and Fox News broke antitrust law with their brief pause in pool coverage.
What we don't: How the department sees the pause as an antitrust violation, and whether it will take legal action.