The US Department of Justice is investigating whether the decision of the White House television press pool to halt coverage of the US president, Donald Trump, last month violated antitrust law, an agency spokesperson said Saturday.

A spokesperson for the department said group boycotts among business competitors might violate US law. “The Antitrust Division is simply investigating to determine whether these news organizations have violated the antitrust laws,” they said.

The announcement came after the television pool of five broadcasters last month ceased presidential coverage after the administration barred CNN, MS Now and Politico from the White House.

Messages were sent late Saturday to the five outlets seeking comment: ABC, CBS, CNN, Fox and NBC.

The White House press pool, which is a rotating cast of news outlets that covers the president, has become a proxy for the wider fight over whether the president, or anyone, can control the content of news reports – a type of free speech, pillar of American democracy.

Last month’s developments marked an extraordinary escalation in Trump’s efforts to restrict news reporters and outlets that he finds insufficiently supportive.

On 19 September, the White House blocked reporters from CNN, Politico and MS Now from entering the building, ​revoking their credentials. The White House said covering the president was a “privilege – not a right”.

CNN, MS Now and Politico sued over the days-long ban. It was lifted after a judge handed the three news organisations a reprieve, which is in place until Tuesday.

Television pool coverage of the White House has also resumed. They broadcasters in the pool share the costs of covering the president, take ​turns organizing coverage and share ​the footage with outlets around the country.

Jose Zamora, the Committee to Protect Journalists’ regional director of the Americas, on Saturday criticized the administration’s decision to investigate.

“The government should not use antitrust investigations to intimidate news outlets defending press access,” Zamora said on X. “The public’s right to know depends on that access.”