SAN FRANCISCO — The American Civil Liberties Union of Northern California on Wednesday filed suit against U.S. Immigration and Customs Enforcement in an effort to reveal more information about the agency's use of automated license plate reader technology.

The Freedom of Information Act lawsuit, filed in the U.S. District Court for the Northern District of California, comes after it became known earlier this year that ICE contracted with companies to gain access to private automatic license plate reader databases.

The ACLU's Northern California branch subsequently filed two FOIA requests relating to ICE's use of the databases. The requests, filed on on March 19 and March 21, sought more information about the contracts, ICE's privacy policies, and the agency's use of the data.

But in a press release, the organization said ICE has “improperly withheld the requested records.”

“Aggregation of this information into databases containing billions of license plate scans stretching back months and even years threatens core civil rights and liberties protected by the Constitution,” the ACLU said. “While police departments collect the data for local criminal investigations, ICE may now be using the data for civil immigration enforcement.”

Danielle Bennett, a spokeswoman for ICE, said the agency does not comment on pending litigation. But she also sought to tamp down the notion that ICE's use of license plate reader technology is out of the ordinary.

“Like most other law enforcement agencies, ICE uses information obtained from license plate readers as one tool in support of its investigations,” Bennett said in an email. “ICE conducts both criminal investigations and civil immigration enforcement investigations. ICE is not seeking to build a license plate reader database, and will not collect nor contribute any data to a national public or private database.”

She said ICE completed a privacy impact assessment in 2015 that was then used to create a framework for use of license plate reader technology.

“The privacy impact assessment was updated prior to ICE's use of any license plate reader database, to reflect how the contract meets the established privacy requirements,” Bennett added, calling them the “most stringent requirements known to have been applied for the use of this technology.”

The ACLU and the Electronic Frontier Foundation last year succeeded in convincing the California Supreme Court they should be able to access certain automated license plate reader data gathered by police in California cities, as part of a project to show how pervasively the technology can track individuals and their movements.

The state high court, however, denied the organizations' request to access to raw license plate data. Instead, it said they must work out at the trial court how to best anonymize the information, in order to avoid jeopardizing the privacy interests of individuals whose plates were captured.

The new case against ICE is American Civil Liberties Union of Northern California v. U.S. Immigration and Customs Enforcement. The lead lawyer for the ACLU of Northern California on the case is staff attorney Vasudha Talla.