Since at least 2010, the Drug Enforcement Agency (DEA) has been expanding a regional license plate reader (LPR) program to the entire United States. Previously the program was only known to be concentrated in the border region of the American Southwest.

The revelation comes from new documents obtained and published late Monday by the American Civil Liberties Union (ACLU) under the Freedom of Information Act. The documents also show the DEA captured over 793 million license plates from May 2009 through May 2013 with the stated goal of drug-related asset forfeiture.

"The government has essentially created a program of mass tracking," Catherine Crump, a former ACLU lawyer who now teaches at the University of California, Berkeley, told Ars. "The US has created a system where the government can track you and the American public simply has to accept it as a fait accompli."

LPRs scan plates at very high speed—often 60 plates per second—and record the date, time, and precise location that a given plate was seen. On a patrol car, that plate is then immediately compared to a list of wanted or stolen cars, and if a match is found, the software alerts the officer.

Law enforcement has argued as recently as last week that such records are indispensable for recovering stolen cars and for using in criminal investigations. The devices are rapidly being deployed by state and local law enforcement agencies—notably some communities (such as the wealthy small town of Piedmont, California) have even put them up as an electronic border against their neighboring towns.

The Department of Justice, the DEA’s parent agency, did not immediately respond to Ars’ specific questions sent by e-mail.

UPDATE 2:18pm CT: Patrick Rodenbush did not respond to Ars' questions, but sent this statement: "It is not new that the DEA uses the license plate reader program to arrest criminals and stop the flow of drugs in areas of high trafficking intensity. This program includes protocols that limit who can access the database and all of the license plate information is deleted after 90 days."

Another e-mail dated June 1 2010, presumably from within the DEA, states that the agency’s LPR pilot program was:

...officially opened to all of DEA and our Federal, State, and Local counterparts. The Pilot National LPR Initiative has received enormous support from several government and law enforcement entities and multiple request have been made to connect LPR devices from state and local law enforcement In anticipation of the Pilot National LPR Initiative being utilized by all of DEA as well as Federal, State, and Local law enforcement throughout the United States we must insure we can collect, manage, and maintain to the highest standards all data from the system as well as every other aspect of the LPR system. DEA has designed this program to assist with locating, identifying, and seizing bulk currency, guns, and other illicit contraband moving along the southwest border and throughout the United States. With that said, we want to Insure we can collect and manage all the data and IT responsibilities that will come with the work to insure the program meets its goals, of which asset forfeiture is primary.

One question that often comes up in discussions of such records is how long such data should be retained. In 2012, the DEA decided that it would reduce its retention period from two years to six months.

Such data retention policies by various law enforcement agencies vary widely. For example, in California, the wealthy city of Menlo Park (home to Facebook) retains data for just 30 days, while the Los Angeles Police Department (LAPD) retains data for two years. By contrast, Oakland, just across the bay from San Francisco, has no retention limit.

This week, lawmakers in Minnesota continued debate as to whether the data should be held for 90 days or deleted immediately if no “hit” for a stolen or wanted car is found.

"I think the other thing that's notable about this is that you're now seeing the creep of technology and mass surveillance beyond the terrorism rationale into routine law enforcement," Crump added.