The US Department of Justice is investigating five television networks after they briefly suspended their pool coverage of President Donald Trump, US media reported on Saturday.
Trump barred CNN, MS NOW and Politico from the White House last month for distributing what he called "fake news" and "fiction and lies," a decision later reversed by a federal judge.
At the time, the top five US broadcasters halted pool coverage of the White House -- where a broadcaster films on behalf of all television outlets -- for several days in solidarity with CNN.
The pool is a rotating group of journalists that travel with the president and provide coverage to other outlets, due to limited space.
Officials from the Justice Department contacted the networks on Friday and demanded communications and materials related to the White House TV pool, the New York Times reported, citing six people with knowledge of the action.
Justice Department spokeswoman Emily Covington told the Times and the Washington Post that the five networks -- ABC, CBS, CNN, NBC and Fox News -- had "boycotted covering White House events."
"Group boycotts among commercial competitors can violate the Sherman Act," an antitrust measure, Covington wrote in a statement.
"The Antitrust Division is simply investigating to determine whether these news organizations have violated the antitrust laws."
Trump has long attacked media that have aired critical coverage of him, repeatedly blasting the press as the "enemy of the people."
Bruce D. Brown, president of the Reporters Committee for Freedom of the Press, said the Justice Department probe "appears to be a pretext for seeking records from the networks about how they are covering daily White House events during a media ban the president himself put in place."
"The decisions news organizations make about coverage are protected by the First Amendment, and summoning antitrust authority... is another and even more brazen attempt to try to intimidate journalists," Brown said in a statement.
On Thursday, CNN, MS NOW and Politico appeared in a downtown Washington court to urge a federal judge to extend their White House access.