Newport News, Va., Sheriff’s Deputy Robert Forrest with an automatic license plate reader. (AP/Joe Fudge)

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 and civil liberties critics say can be used to track the movements of innocent people.

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. The devices, typically mounted on the back of police cars, can capture hundreds of license plates per minute and check them against a database of stolen or wanted vehicles. Each photo also notes the exact time and place it was taken, and police have been able to review the data later to find missing persons or solve serious crimes.

But critics say that 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. Only 14 states have laws addressing the use of license plate readers at all, according to the National Conference of State Legislatures, and just eight of those address how long the police can maintain the data. California limits the time to 60 days. New Hampshire’s law states that the data “shall be purged from the system within 3 minutes” unless it triggers a related action. Colorado allows police to keep the records for three years.

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 law’s definition of personal information includes an “agency-issued identification number,” but one judge has concluded that license plates – in plain view for anyone to see – don’t qualify.

After a bill to limit the data retention time to seven days was vetoed by Va. Governor Terry McAuliffe (D) in 2015, the ACLU filed suit in Fairfax on behalf of Harrison Neal, whose license plate had been captured twice by police cameras. The suit sought to prohibit the Fairfax police from keeping the information at all, a practice the Virginia State Police began after receiving an opinion from then-Attorney General Ken Cuccinelli (R) that retaining the information violated the Data Act. Fairfax keeps its license plate data for a year.

The ACLU and Fairfax argued over whether a license plate was personal information, particularly if it is displayed on a vehicle operating on a public roadway in view of everyone. Fairfax Circuit Court Judge Robert J. Smith ruled last November that the plates were not personal information, in part because federal appeals courts had ruled that there was “no privacy interest in a license plate number.” He dismissed the ACLU’s suit.

The ACLU appealed to the Virginia Supreme Court, which decided last week to hear the case. The ACLU’s first brief is due August 1, and in addition to Fairfax’s reply brief other interested groups such as the Electronic Frontier Foundation are likely to file amicus briefs. Though a ruling would be binding only on Virginia, it could have “nationwide impact as other states begin litigating these privacy issues,” said ACLU lawyer Hope Amezquita. “As modern technology evolves and law enforcement uses it more and more, there’s got to be checks and balances and real regard for the privacy rights of innocent citizens.”

A related issue with the license plate readers is the question of who may see or have access to the vast data created by them, an issue which also has arisen with body-worn cameras on officers. One Northern California agency reported it had collected information on 3.2 million license plates in just three months. The ACLU and the Electronic Frontier Foundation, seeking access to data kept by Los Angeles police, argued their case to the California Supreme Court earlier this month.