U.S. Immigration and Customs Enforcement is using sophisticated technology to keep tabs on immigrants, privacy advocates say, raising concerns about the breadth of ICE surveillance activities.

The American Civil Liberties Union released a detailed report on ICE’s efforts to track immigrants using what it called an “expansive surveillance database” with information from automated license plate reader tools, offered by a company called Vigilant Solutions. The ACLU report, based on a Freedom of Information Act lawsuit filed in May 2018, accused local law enforcement agencies of sharing information with ICE, sometimes in violation of local privacy laws.