A policewoman talking into her cellphone while driving pulled over a disapproving motorist just to tell him she was exempt from the phone ban, he says.

North Shore man Shawn Hill says he passed the policewoman while sitting in the passenger seat as his partner drove over the harbour bridge just before 7am on Saturday.

Mr Hill turned back to look at the officer and exclaimed to his partner: "She's on the phone!"

Mr Hill thinks the officer took him to be mouthing at her, telling her to get off the phone, because the patrol car flashed its lights and pulled his car over just past the Cook St exit.

The officer walked up to the passenger-side window and told him police had an exemption to allow them to use their cellphones while driving and she did not appreciate being told off, Mr Hill said.

"There's been a debate about this and I think police should be using cellphones only for emergencies," Mr Hill said.

He said the policewoman's phone use could not have been for an emergency because she had time to slow down and follow him for a while.

"It's certainly not on," he said. "I just thought that police could only pull people over if it was for a specific reason."

Mr Hill said he had had only pleasant experiences with police in the past but the incident on Saturday had been "displeasing".

"She had a bee up her bonnet. She was annoyed," he said.

Police brand manager Annie Coughlan would say only that under the land transport legislation, officers were exempt from the rules barring motorists from using cellphones.

The Land Transport (Road User) Amendment Act 2009 says: "An enforcement officer may, while driving a vehicle, use a mobile phone to make, receive, or terminate a telephone call if ... [it is] in the execution of the officer's duty."

The legislation does not specify the reasons police officers can pull over drivers.

This year, a senior officer told the Herald it was a joke for police to go out and enforce the cellphone ban when they appeared to be flouting it by using their phones behind the wheel.

"I am absolutely pissed off by the hypocrisy," the officer said.

The comments followed the publication of images of what appeared to be police officers talking on their phones while driving.