The FBI likely has a fleet of license plate readers that it loans to local police departments, though there has been an internal debate at the bureau over whether the system constitutes an invasion of privacy. That’s according to documents published Friday by the American Civil Liberties Union, a disclosure that comes amid a growing debate over domestic surveillance.

Privacy advocates have warned that the national license plate database enables police to track vehicles in near real-time, and data collected over a number of months would provide law enforcement with a near-complete picture of an individual’s daily activity. Federal and local police have kept quiet on the issue even as it made its way into court. Now, though, documents obtained by the ACLU include emails from the FBI’s Office of General Counsel saying bureau lawyers paused the program in 2012 because they were “wrestling with [license plate reader] privacy issues.”

“Once these issues have been resolved…hopefully this Summer…we expect to be back,” one FBI employee wrote. “The program is still growing and we enjoy tremendous field support.”

It’s not clear what the “issues” mentioned were or what privacy issues the FBI documents referred to.

“Nothing has been released to the public to suggest that solutions are being implemented,” wrote Bennett Stein of the ACLU Speech, Privacy and Technology Project. “While internal discussion [about privacy matters] is unquestionably a good thing, it is by no means sufficient. The public has a right to know what information about non-suspects is collected, how long it is retained, whether it is shared with other agencies or departments and for what reasons, and what oversight mechanisms.”