They say there are privacy concerns created by the increasing use of automated license plate readers.
The devices can scan the license plates of thousands of vehicles per hour.
They look for everything from unpaid tickets to stolen cars.
The ACLU wants to know if information gathered about where a car is parked and for how long could be used to track a person's movement.
"The problem with all of this technology is if there aren't regulations and audits in place, the harms never come to light," said the ACLU's Karen Sheley. "So if someone's privacy is invaded they're likely never to find out on their own."
A Chicago police spokesperson said that license plate readers have helped recover more than 1,000 stolen cars and arrest 700 offenders in recent years.
Police say information about vehicles without violation is generally deleted after two weeks.