CNN, MS NOW and Politico to file lawsuit against Trump's White House ban
The US media outlets say they are defending "the principle that the government does not decide what the press reports or publishes".
CNN, Politico and MS NOW have said they will sue the Trump administration after being barred from the White House.
President Donald Trump announced the ban on Friday, accusing the three organisations of writing "fiction or lies" about his government.
The companies said their reporters were denied entry and had their badges taken when they tried to access the building on Saturday.
In a joint statement on Monday, they said they were taking legal action to "protect our First Amendment rights and defend the principle that the government does not decide what the press reports or publishes".
The First Amendment bars the government from "abridging" freedom of the press — wording that courts have traditionally understood as stopping the government from discriminating against media outlets on the basis of the content of their coverage.
"Without notice or process, the White House revoked our journalists' credentials because it objected to our reporting," the CNN, Politico and MS NOW statement continued.
"Left unchallenged, this threatens press freedom and the public's right to independent journalism free from government interference."
When announcing the ban last week, Trump did not cite any specific stories or reporting that led to the move, but later said "it's really just cumulative stories over the last few years".
The US president added that there "may be others to join them".
When later asked by a reporter what he meant, Trump replied: "Others to come in terms of fake news? Well, you know, the New York Times is fake news, the Washington Post is fake news."
He has often criticised news organisations, and his administration has brought legal action against several outlets, including the New York Times, the Wall Street Journal and the BBC.
Some of those lawsuits have ended with media organisations agreeing to multimillion dollar settlements. Trump's lawsuit against the BBC is still ongoing.