The Virginia Supreme Court has agreed to hear a challenge over how long police can keep data from automated license plate readers, which police say can provide valuable investigative information.

The case, filed by the American Civil Liberties Union in Fairfax County, Va., appears to be the first legal challenge in the nation to the varying lengths of time police retain the data recording when and where a vehicle is photographed by a license plate reader.

Critics say keeping the data beyond a short period of time amounts to “mass surveillance” and creates the possibility for abuse by police or others who can access the data, by creating a trail of personal movement.

Virginia has no law specifically addressing license plate readers. But it does have the “Government Data Collection and Dissemination Practices Act,” commonly referred to as “the Data Act,” which says that government agencies “shall not collect personal information except as explicitly or implicitly authorized by law.”

The key question is whether a license plate contains “personal information,” the Washington Post reports.