The photographers held a mass photo call in protest at the law
Hundreds of photographers have staged a protest outside Scotland Yard against a new law which they say could stop them taking pictures of the police.
The law makes it an offence to gather information on security personnel if that data could be used for a purpose linked to terrorism.
The National Union of Journalists said the law could be used to harass photographers working legitimately.
The Home Office said it was designed to protect counter-terrorism officers.
The NUJ wants the government to issue guidance to police forces on how exactly the law should be used by individual officers on the ground.
'Treated as terrorists'
The photographers, both professional and amateur, held a mass photo-call outside the Met Police headquarters at Scotland Yard on Monday.
They are angry at the introduction of Section 76 of the Counter Terrorism Act and argue it can be used by police to stop and search them in any situation.
It makes it an offence to "elicit, publish or communicate information" relating to members of the Armed Forces, intelligence services and police, which is "likely to be useful to a person committing or preparing an act of terrorism".
Vice President of the NUJ Pete Murray said it was absurd to treat photographers as terrorists simply for doing their job.
"If the police officer isn't doing anything wrong then what are they worried about?" he told the BBC.
"I mean, we as citizens constantly get told that these extra security laws, terrorism laws, all of this surveillance stuff, is not a threat to us if we're not doing anything wrong.
"So why on earth it becomes a threat to a police officer to have a photographer, a working journalist, a photographer taking a picture of them is quite beyond me."
He said that even if an officer were in the background of a shot - for example, at a football match or street parade - "the photographer may end up on the wrong side of the law".
Peter Smyth, chairman of the Metropolitan Police Federation, backed a call by Grimsby MP Austin Mitchell to introduce a formal code to clarify the position of both the police and photographers.
"Its aim should be to facilitate photography wherever possible, rather than seek reasons to bar it," he said.
Critics say the law will prevent them reporting on legitimate protests
"Police and photographers share the streets and the Met Federation earnestly wants to see them doing so harmoniously.
"As things stand, there is a real risk of photographers being hampered in carrying out their legitimate work and of police officers facing opprobrium for carrying out what they genuinely, if mistakenly, believe are duties imposed on them by the law."
In a statement, the Home Office said taking pictures of police officers would only be deemed an offence in "very exceptional circumstances".
"The new offence is intended to help protect those in the front line of our counter terrorism operations from terrorist attack," it said.
"For the offence to be committed, the information would have to raise a reasonable suspicion that it was intended to be used to provide practical assistance to terrorists."
The Home Office added that anyone accused under the act could defend themselves by proving they had "a reasonable excuse" for taking the picture.
Anyone convicted under Section 76 could face a fine or a maximum of 10 years' imprisonment.