Six journalists are suing Scotland Yard over claims surveillance information on them was recorded on a database designed to monitor so-called "domestic extremists".
Times journalist Jules Mattsson, comedian and journalist Mark Thomas and four photographers - Jason Parkinson, Jess Hurd, David Hoffman and Adrian Arbib - are taking legal action against the Metropolitan Police Commissioner and Home Secretary, the National Union of Journalists (NUJ) said.
The Times newspaper previously reported that Scotland Yard's Police National Domestic Extremism and Disorder Intelligence Unit holds 2,000 records which relate to photographers and journalists.
The NUJ has instructed Bhatt Murphy Solicitors to challenge the surveillance and retention of its members' data on the basis it is unnecessary, disproportionate and not in accordance with the law.
Michelle Stanistreet, NUJ general secretary, said: "It is outrageous that the police are using their resources and wide-ranging powers to put journalists under surveillance and to compile information about their movements and work on secret databases."