CNN, MS NOW and Politico say they have told Donald Trump's administration that they are filing a lawsuit over being denied White House access.
Reporters from the three news organisations were blocked from the White House on Saturday, local time, a day after Mr Trump said he was barring them because of reporting he found to be "fake news".
"Without notice or process, the White House revoked our journalists' credentials because it objected to our reporting," the outlets said in a joint statement posted on X on Monday.
All three had before hinted at legal action.
White House Correspondents' Association president Jacqui Heinrich called on the Trump administration to at once restore access.
On Friday, local time, Mr Trump said he would ban all three outlets because of coverage he disliked.
White House reporters from the two cable networks went live to report they had been turned away, their press badges deactivated, when arriving for their jobs at the White House on Saturday.
Soon after, Politico said its White House reporter Cheyenne Haslett was also denied entry and had her badge confiscated.
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