The Justice Department's Antitrust Division is investigating whether ABC, CBS, CNN, NBC and Fox News broke federal antitrust law when they stopped sharing pooled television coverage of President Trump for several days in September. ABC, CBS, Fox News and NBC had refused to fill in after the White House kept CNN from its scheduled pool duties, a show of solidarity with CNN that the department now calls a boycott.

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

The Times, citing six people with knowledge of the matter, reported that officials reached out to the networks on Friday and asked for communication records and other material tied to the pause. Variety, drawing on its own sources, said the department had told the five networks it plans to investigate and had notified several of them that day. The networks declined to comment or did not respond to Variety, and The Desk, a trade publication covering broadcast and streaming media, noted that none of the five had released a statement.

The confrontation dates to Sept. 18, when Trump said he was barring CNN, Politico and MS NOW from the White House over what he called "purposely negative stories." The three outlets sued on First and Fifth Amendment grounds. The television pool stopped operating on Sept. 21, when the White House would not let CNN work its assigned shift. Several of the president's events went without the shared network video that outlets around the world normally use, including Chinese President Xi Jinping's White House visit on Sept. 24, which had no network pool coverage.

The pool resumed on Sept. 25, a day after U.S. District Judge Timothy Kelly ordered the administration to restore the three outlets' access. Kelly found in that initial order that the outlets were likely to succeed on their claim that they had been denied due process. On Thursday he extended the temporary order and said he expects to rule by Tuesday on their request for a preliminary injunction. Government lawyers have defended the ban on national security grounds, and the White House has accused the outlets of spreading false information and publishing sensitive material. The outlets say those justifications were offered after Trump had already decided to punish them for reporting he did not like.

The three outlets now have their credentials back, but the administration has begun arguing that they have no guaranteed access to particular places such as the Oval Office or Air Force One. Politico was kept off an Air Force One trip this week despite its restored credentials, and other news organizations declined to take its seat.

Pooling exists because many events happen in spaces too small for every news organization. The arrangement gives participating outlets equal access to the same video, photographs and transcripts, and wire services, newspapers and magazines take part alongside the television networks, according to Variety. NBC News recently took over coordination of White House pool coverage from Fox News under a rotation that changes every three months, the outlet reported, citing two people familiar with the matter.

Variety questioned whether the department has legal standing, noting that the networks have coordinated pool coverage for decades without any legal challenge to the arrangement. It also reported that the networks kept covering the White House and the president throughout the pause. The Desk observed that federal antitrust law generally bars certain coordination among competing businesses, but that such a case can be harder to prove when the coordinated conduct hurts the participants rather than giving them an edge over a rival.

For now the department has filed nothing. The Desk reported that no civil action has begun and that it is unclear whether the administration will take the matter to court.