San Leandro, Calif. (CNN) - Law enforcement agencies from around the country are using license plate readers to track millions of vehicles.
The cameras are mounted on bridges of police cruisers and can help police locate a vehicle that has been stolen or involved in a crime.
According to a report released Wednesday by the ACU, they also track the movements of vehicles not on "hot lists."
The ACLU is calling for legislation that would require law enforcement agencies to adhere to strict rules while collecting the data.
Mike Katz-Lacabe, a San Leandro, Calif. activist, petitioned the police department and got a hold of the records on his car, and was stunned by what he saw.
Although Katz-Lacabe did not face criminal charges and had not been accused of any crimes, he became shocked by the amount of information the San Leandro Police Department had about him, including a photograph of him and his daughters.
Katz-Lacabe found what he said is an egregious violation of privacy: In 112 instances over two years, police just happened to get images of his car and more.
"I do think big brother has gone too far, because i have not been charged with, I'm not suspected of committing any crime," Katz-Lacabe said.
Any time a police officer drives a car with the technology, the scanners are recording and storing the license plate information on servers. Jeff Tudor, a San Leandro officer, said "with technology and with smart, good policing, it allows us to keep our citizens safe."
Police said the data can later be accessed to solve all types of crimes, allowing them to follow leads on amber alerts and collect unpaid tickets.
However Katz-lacabe said the technology crosses the line.
"Innocent people should not have their records being stored by law enforcement," Katz-Lacabe said.
Many law enforcement agencies have embraced this technology, as more than a third of large police agencies are using automated plate readers, according to a 2010 study by George Mason University. Many cars have three cameras: One on the roof, one on the left, one on the right, and one on the side. They capture plates instantaneously. Those plates are then cross-checked against suspect vehicles, so if a car comes across as being stolen, the officer will be instantly alerted.
Many critics do not object to the data collection, but oppose departments' ability to keep the information on file for months or years.
Privacy rights groups have filed a lawsuit against two major police departments in Los Angeles County over such scanners.
The lawsuits claim the agencies refused to turn over information collected by such scanners.
Jennifer Lynch of the Electronic Frontier Foundation said "once they have the location of your plate and where you were on that date and time that they scanned your plate, they can see where you work, who you associate with, where you pray, where you're going to the doctor, and they can learn quite a lot about you."
"In order to have a discussion about something like this, people have to know what's happening," Katz-McCabe said.
Police said the technology has only been used against crime suspects, but in this new era of digital rights and privacy, some groups said they would like to see more transparency and limits to what information can be gathered and stored on citizens doing nothing more than driving their cars.