ACT Policing and the ACT Road Transport Authority were given the instruction when a motorist this month mounted a successful legal challenge over a traffic offence committed several years ago.

It prompted ACT Law Society criminal law committee chairman Michael Kukulies-Smith to condemn the process as "an ill-advised piece of action" that was hard to justify such a long time after drivers committed an offence.

Hundreds of Canberra motorists have received letters in recent weeks that said records showed they hadn't paid overdue traffic infringements handed out in the past eight years.

The notices warned the drivers their licences would be cancelled next month if they didn't pay up or make their case for the outstanding fines to be scrapped.

ACT Policing has not confirmed how many people received the letters, but it's believed they went out to more than 1500 drivers.

Angry motorists who complained said they spent hours on the phone being passed between government agencies and police as they slammed the notices as "bureaucracy gone mad" and a "money grab".

ACT Policing blamed the delay on a computer glitch that meant 7000 traffic fines issued in the territory hadn't been linked to a client record on the RTA RegoACT database.

Documents showed one motorist's fine was withdrawn after police acted on legal advice that it was unreasonable to think the Road Transport Act allowed a person to be prosecuted for an offence based on a reminder notice issued years later.

The documents said police had also considered a section of the Human Rights Act that stated anyone charged with an offence had a right to be tried "without reasonable delay".

Mr Kukulies-Smith, a partner at Kamy Saeedi Law, acted on behalf of that client and said the letters sent to drivers were misleading and put the onus on drivers to prove they didn't commit the offence or had already paid the fine."It goes against basic principles of criminal justice to make an accused person prove they should not be forced to pay the fine," he said.

"The withdrawal of matters we have challenged has revealed the advice the RTA has received confirms the pursuit of these matters years later is unreasonable."

It was also a concession the authority accepted the action was "likely unlawful", Mr Kukulies-Smith said.

"People receiving these notices should contact an experienced criminal lawyer immediately or they risk losing their licence."

One Hawker motorist has vowed to challenge about 20 reissued fines for ACT offences that dated as far back as 1998.

The man said he had paid each fine to his knowledge but because his bank records didn't go back that far he had little to prove it.

"I don't really have any records except that my rego and licence have been renewed many times in the ACT over the years and I would not have been able to do that if I hadn't paid those fines," he said.

"It's an impossible waste of court resources because I'm going to have to dispute each one, one by one, and take it to court and find out whether they have any evidence to support that fine."

An ACT Policing spokesman said information on how to pay, request a withdrawal or dispute the fine was included on the back of the notices.