The Justice Department is investigating whether the major TV networks, including CBS, violated antitrust laws after they briefly suspended the television press pool system in response to President Trump’s decision last month to ban three news organizations from the White House.

“Members of the television press pool have boycotted covering White House events,” Justice Department spokesperson Emily Covington said in a statement provided to CBS News on Saturday. “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.”

It was not immediately clear how the Justice Department was defining the move as a violation of the Sherman Act, which is a longstanding federal law that seeks to prevent monopolistic business behavior and maintain fair competition.

The New York Times was first to report the investigation. CBS News has reached out to the White House and all five networks — ABC, CBS, CNN, Fox and NBC — for comment.

In mid-September, Mr. Trump announced that his administration was rescinding the White House credentials of journalists for CNN, MSNOW and Politico over what he alleged was “their constant ‘reporting’ FAKE NEWS!”

The White House also sent letters to each of the three news outlets informing them that certain articles they had published on topics including the new White House ballroom, the ongoing war with Iran and the Republican midterm convention were threats to national security and violated standards of “professionalism and decorum” for reporters. 

Following the move, the five networks that make up the TV press pool jointly announced that they would be suspending their coverage in solidarity. That suspension occurred at a critical moment in that it coincided with Chinese President Xi Jinping’s state visit to Washington.

In a group statement at the time, the five networks said, “The public has a vital interest in receiving accurate, independent information about its government. No administration should reject a news organization because it objects to its reporting.” 

The TV press pool covers the president’s travel and events on a rotating basis, providing video to other news organizations.

CNN, MSNOW and Politico immediately filed a lawsuit to have their access restored, and U.S. District Judge Timothy Kelly subsequently granted a temporary restraining order against the president’s ban, and their credentials were reinstated.

However, despite having their credentials restored, the White House has continued to refuse to allow CNN and Politico into the Oval Office or aboard Air Force One.

That restraining order was set to expire on Thursday, but Kelly extended it to next Tuesday while he continues to consider the case.

CBS News and CNN are both part of Skydance, the parent company formed following the merger of Paramount and Warner Bros. Discovery that was finalized earlier this week.