News outlet MS Now said its journalists were denied access to the White House grounds on Saturday morning, a day after Donald Trump said he would ban the news channel and two other news outlets, CNN and Politico, from the executive branch complex.

The outlet said a reporter and a cameraman had been denied access and had their White House press passes confiscated by the US Secret Service at a security gate outside the West Wing.

“The White House belongs to the American people and the decisions made inside are funded by our tax dollars,” MS Now said, adding that it “intends to take any and all steps necessary to defend our first amendment rights and the essential role of independent journalism in our democracy.

“We stand firmly behind our anchors, our reporters and our newsroom. We will continue to report on the president, the administration and the issues that impact the American people.”

Trump’s threat to banish CNN, MS Now and Politico from the White House has brought condemnation from first amendment advocates and Democratic officials, among others, as the conflict between the US president and parts of the media sharply escalates ahead of November’s midterm elections. It has also thrown into stark relief Trump’s attack on press freedom in the US, which has unnerved civil liberties advocates.

In a Truth Social post on Friday afternoon, Trump said he would order the removal of the news outlets “effective immediately” for what he claimed was “constant ‘reporting’ FAKE NEWS!” and said he is considering banning more. Trump did not identify a single infraction, but rather said his decision was “really just cumulative stories over the last two years. You get sick of it.”

The White House Correspondents’ Association, which represents the White House press corps, condemned the move. “The constitution protects the freedom of the press from government interference,” it said on social media. “That protection does not depend on whether the president likes a news organization’s coverage, agrees with its reporting or approves of the questions its journalists ask.”

The body said the issue is “about more than the rights of journalists” but about “the right of the American people to receive a full and independent account of the activities, policies and decisions of whoever occupies the nation’s highest office”.

Trump has long clashed with the media over what he considers slanted coverage of his administration and himself personally, as well as describing a media environment in which the press and his political opponents are in collusion.

Last year the Associated Press was banned form the White House after refusing to acknowledge an executive order changing the name of the Gulf of Mexico to Gulf of America.

After Friday’s ban was announced, CNN issued a statement saying that removing its reporters from the grounds could violate the law.

“CNN stands fully behind our White House team and their fair and accurate reporting,” a spokesperson for the outlet said. “We have a right under the US constitution to do that reporting without hindrance or interference from the government.”

Politico also issued a statement, saying it would “continue to fairly report on this White House and future ones” and “will vigorously defend our first amendment rights against any attempt to restrict them”.

Jim Acosta, a former CNN reporter, accused Trump of “taking a meat axe to the free press in this country”. Speaking on MS Now on Friday, Acosta called the latest media bans “a slippery slope” and warned: “We are on the path to having a state media-like system in this country.”

Acosta said the media should collectively oppose Trump’s ban. “Each of these news organizations should sue the White House, sue Donald Trump, and that other news organizations in Washington should band together and say, ‘We will not go to the White House and cover you and cover your administration. We’re banning you.’”

Press freedom group PEN America said: “Someone needs to explain to President Trump how the first amendment works. As we’ve seen time and time again, this administration’s hostility toward the press is never about the accuracy of news stories, but about its inability to withstand scrutiny of its actions. The White House can’t be allowed to decide which journalists are able to cover the president based on the content of their news coverage.”