Greater Manchester Police has reminded its officers that they must not stop the press from taking photographs in public places following an alleged assault on a photographer by two officers in Oldham Last week.
Stuart Littleford, editor of the Government and Public Sector Journal, claims he was assaulted by two police officers while taking photographs of a road accident.
GMP's Professional Practices Board has launched an inquiry.
A spokeswoman said: "Greater Manchester Police respects the rights of journalists and has previously issued guidance to officers about journalistic rights.
"That advice will be reiterated to all officers. It would not be appropriate to comment further pending the outcome of the complaint investigation."
Littleford said he may sue for damages over injuries to his hands and legs and has the backing of the Chartered Institute of Journalists.
The incident happened last Thursday at 2pm, when he stopped at a crash scene in Egerton Street, Oldham.
A woman had been hit by a car and Littleford stopped to help because he has medical experience.
Littleford then tried to take a photograph of the accident scene, but a police officer at a cordon said he could not take photos.
He said: "I told him I was from the press and also showed him my press card. I was doing my job in a lawful manner. He grabbed me by my lapels and threw me to the side of the road, then blocked my view to stop me taking any shots.
"The officer had absolutely no respect for the ACPO-recognised press card."
Littleford said he then tried to report the assault to a police traffic officer.
He said: "He refused to give me any details. I turned on my video camera and he immediately jumped out of the car and said: 'I have not given you permission to take my photograph'.
'He grabbed my phone and smashed my hand repeatedly against the police car in an attempt to smash the phone.'"
He added: "He was like a mad man. They would have gone to any length to take anything off my phone.
"It was really scary. I felt intimidated, humiliated and have suffered physical injuries as a result of these assaults."
He added: "I feel unable to safely do my job as an editor and a journalist in Manchester now.
"If this is the way a journalist and editor with a press pass is treated in a public place, for nothing more than just doing his job, God help anyone else."
In May 2010, Littleford complained that he was assaulted by a police officer whilst filming at incident in Oldham.
Guidelines issued by the Metropolitan Police state: "Members of the public and the media do not need a permit to film or photograph in public places and police have no power to stop them filming or photographing incidents or police personnel."