The American Civil Liberties Union is suing Immigration and Customs Enforcement and Customs and Border Protection, alleging the two agencies failed to turn over data on how they’re using cellphone surveillance technology.

After a December 2016 congressional report indicated that the controversial Department of Homeland Security agencies spent millions of dollars to acquire dozens of Stingray devices each, the ACLU filed Freedom of Information Act requests to determine how the agencies were using them, according to a complaint filed in the case Wednesday. Those devices, also known as IMSI catchers (for the international mobile subscriber identity number used to identify cellphone users), impersonate phone towers to determine where cellphone users are located and, sometimes, to observe call records and text messages.

“The public has a right to know if and how often ICE and CBP are using Stingrays, which were originally intended for use by the military and intelligence agencies, for civil immigration enforcement operations,” wrote ACLU officials in a blog post announcing the lawsuit. “We also have a right to know if the agencies have taken any steps to protect the privacy of bystanders swept up by Stingrays, whether they inform people in immigration court proceedings when a Stingray has been used against them, and what limits, if any, exist on the use of this technology.”

ICE told the ACLU it couldn’t find relevant records and then ceased to respond, according to the complaint, despite at least two instances where the agency is known to have obtained warrants to use the devices to find particular undocumented immigrants. CBP similarly said it didn’t have relevant records, despite the congressional report saying it had at least 33 Stingray devices as of 2016.

A spokesperson for ICE declined to comment, citing a policy of not discussing pending litigation. CBP also declined comment for the same reason.

In its lawsuit, the ACLU is asking a federal court to order the agencies to “conduct adequate searches” for relevant records and quickly turn them over.

Stingrays have been used by police agencies around the country, often with little information provided to the public about how and when they’re used. DHS also warned last year that unauthorized Stingrays have been detected around the Washington, D.C., area, leading to speculation that such devices may have been placed by foreign spies.