The US justice department (DoJ) says it is investigating several television networks over whether they broke federal competition laws when they recently suspended pool coverage of President Donald Trump.

The agency has asked ABC, CBS, CNN, NBC and Fox News to hand over communications related to the White House TV pool, a system where networks switch off covering the president and providing the footage to other publications.

The networks temporarily suspended this system last month for several days after the president blocked CNN, MS Now and Politico from the White House.

Members of the pool share their material – pictures and descriptions of the president’s movements – with the wider media.

“Group boycotts among commercial competitors ​can violate the Sherman Act,” a DoJ spokesperson said, referring to the federal law that bars companies from engaging in monopolistic business practices.

“The Antitrust Division is simply investigating to determine whether these ​news organisations have violated the antitrust laws.”

Trump blocked CNN, MS Now and Politico from the White House last month after accusing the organisations of writing “fiction or lies” about his team.

The White House later reinstated their access after a ruling from a judge. The three outlets had sued the Trump administration, arguing the restricted access violated their First Amendment rights.

The First Amendment forbids the government from “abridging” the freedom of the press – language that courts have traditionally interpreted as preventing the government from discriminating against the media based on the content of their coverage.

The Trump administration has taken a number of legal actions against news publications in the US, including lawsuits over coverage of the president.

In February, the White House announced it was taking control of the press pool which has access to Trump and had for more than a century been managed by the White House Correspondents’ Association.

The same month, the Trump administration moved to bar Associated Press (AP) reporters and photographers from spaces where access is limited, such as the Oval Office or Air Force One, because of the outlet’s usage of the term “Gulf of Mexico” instead of “Gulf of America”. AP filed a lawsuit and the case remains ongoing.