CNN, Politico and MS NOW have announced they will sue the Trump administration after the three US media outlets were banned from the White House.
President Donald Trump announced the ban on Friday, accusing the organisations of writing "fiction or lies" about his team. The companies said their reporters were denied access to the building on Saturday.
In a joint statement on Monday, they said they were pursuing legal action to "defend the principle that the government does not decide what the press reports".
Major US TV networks later announced they would suspend their White House pooled coverage of Trump ahead of him heading to New York for the United Nations General Assembly.
Trump, reacting to news of the lawsuit, called the news organisations "Third Rate Clowns" and "Crooked and Corrupt Press" that "trivialise and demean" his achievements.
"Fake News people and publications that only write negatively, and who violate our National Security by writing false and defamatory stories with unknown 'sources,' shouldn't be allowed access to the most important Office anywhere in the World," Trump wrote on his Truth Social platform.
He added that "almost without question" his team will file an appeal.
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 statement from CNN, Politico and MS NOW said: "Without notice or process, the White House revoked our journalists' credentials because it objected to our reporting.
"Left unchallenged, this threatens press freedom and the public's right to independent journalism free from government interference."
The media organisations filed the lawsuit on Monday in US District Court in Washington, asking a judge to quickly rule Trump's ban unconstitutional and prevent his aides from enforcing it.
On Monday morning, major US TV networks pulled out of White House pool duties, which sees media organisations share material with each other to save on costs and space when broadcasting presidential events to the American public.
Fox News Washington bureau chief Bryan Boughton, who currently holds a rotating role helping to organise media TV crews covering the White House, wrote in an email seen by the BBC that "effective today, the TV pool will not be covering designated as pool coverage" of President Trump.
The message said the move followed the White House "preventing" CNN from fulfilling its pool duties for Trump's trip to New York and that "there will be no replacement pool put in place".
CNN - one of only five US news outlets in the White House press pool for live television - was originally due to cover Trump's trip to the UN General Assembly in New York on Monday and Tuesday.
But on Monday morning, the five-seat CNN booth in the basement of the White House press area - typically manned throughout the day from the early hours of the morning - was empty and closed. Screens and monitors inside were turned off.
Instead, a CNN crew was outside the secured area of the White House grounds, broadcasting live from a public pavement.
Five TV networks, ABC, CBS, CNN, Fox News and NBC, issued a joint statement: "The public has a vital interest in receiving accurate, independent information about its government.
"No administration should restrict a news organisation because it objects to its reporting."
Those five networks are considered the only ones with the money and infrastructure to distribute live coverage from the White House and presidential events.
For now, the White House media slot has remained vacant and instead the conservative TV outlet, Real America's Voice, was listed as "secondary" crew on Trump's trip to New York.
Several US outlets also announced that they would not participate in coverage of pooled events, with some saying they would not share still images from Trump events either.
Later on Monday, Trump met with New York Mayor Zohran Mamdani for an hour-long discussion. Afterwards, the two held a news conference, which was covered by New York media.
"I told the president that we're going to have all of the members of the press here on the lawn, and that is something that I believe in - is everyone, no matter the opinion or the critique, that we engage," Mamdani said.
Trump continued his criticism of the media, saying that journalists always say that they will boycott, but they "never boycott" him.
Also on Monday, the White House launched a streaming channel on its site called Trump TV, which began by showing remarks from Trump during a visit to Mount Rushmore in July.
Announcing his ban on CNN, Politico and MS NOW last week, Trump did not mention specific stories or reporting that prompted 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 by this, Trump responded: "Others to come in terms of fake news? Well, you know, the New York Times is fake news, the Washington Post is fake news."
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 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.
There have been a few instances of other administrations attempting to limit certain outlets' access.
The Obama administration tried to exclude Fox News from participating in a press pool interview with an administration official in 2009.
But after pushback from the other four networks in the pool, Fox News was granted access. Unlike with Trump's exclusion of CNN, MS Now and Politico, the Obama administration did not try to bar Fox News from all pool coverage, just one specific interview.
Trump has been frequently critical of news organisations and his administration has launched legal action against a series of outlets, including the New York Times, the Wall Street Journal and the BBC.
Some of the lawsuits have resulted in media organisations agreeing to pay multi-million-dollar settlements. Trump's lawsuit against the BBC is ongoing.
