Police forces in Manitoba are increasingly using infrared cameras to crack down on bad drivers and car thieves, but the technology is raising concerns about personal privacy.

There are six infrared cameras being used by Manitoba police forces to scan thousands of licence plates an hour, with the goal of nabbing drivers whose licences have been suspended or are driving unregistered vehicles.

The Winnipeg Police Service has three infrared cameras, the RCMP has two, and the Brandon Police Service has one.

Winnipeg-based privacy lawyer Brian Bowman says the cameras serve a valid purpose, but questions remain unanswered about the licence plate data they collect.

"Is it used and is it put out there in order to track your whereabouts in ways that were not envisioned when licence plates were first brought in?" Bowman told CBC News.

"That's the slippery slope that privacy advocates are going to be concerned about."

Police officials say the technology is very effective combating motor vehicle offences and car theft.

"If you're driving your car down the street, it's not like it's in your private property, it's not in your house," said Sgt. Rob Riffel of the Winnipeg Police Service.

"I don't think you can say you have an expectation of privacy."

But Bowman disagreed.

"Your privacy rights don't go out the window when you go on a public street," he said.

"Why are they collecting the information? How long are they hanging on to it? For what purpose are they going to use it?"

The RCMP told CBC News they nab about 40 "high risk" drivers a month using the scanning technology.

Spokesman Cpl. Miles Hiebert said 75,000 plates have been scanned since the spring.

Most of the charges are related to unregistered vehicles and drivers who have lost their licences. In two cases, police have nabbed people on outstanding criminal warrants, he said.

The RCMP cameras are based in Headingly and Virden but are moved to target events with high traffic volumes.

Hiebert said the technology is being used as part of a two-year pilot program to determine how effective the devices are in a rural setting.