James Martin/CNET

The American Civil Liberties Union filed a lawsuit Wednesday requesting that two US Homeland Security agencies -- Customs and Border Protection and Immigration and Customs Enforcement -- release details on how they've been using powerful phone surveillance tools.

The ACLU is suing after the two agencies declined to provide it with documents related to International Mobile Subscriber Identity, or IMSI, catchers, more commonly known as Stingrays. These devices pretend to be cell towers and connect with nearby phones, intercepting data that details calls, messages and device location.

IMSI catchers can often pull in data from entire neighborhoods, and they're able to obtain sensitive details on people without the people even knowing. Civil liberties and privacy groups have criticized the technology for its invasive surveillance.

The two agencies have denied the ACLU's requests for information since 2017, telling the civil rights organization that "no records responsive to your request were found."

The assertion comes despite the House Oversight Committee finding, in 2016, that ICE had spent $10.6 million on 59 IMSI catchers and CBP had spent $2.5 million on 33 of the devices.

CBP declined to comment on pending litigation. ICE didn't respond to requests for comment.

In its lawsuit, the ACLU also cites two cases where ICE used IMSI catchers to track and arrest immigrants. Those cases came to light only because journalists uncovered warrants to use the devices.

In its initial request, the ACLU asked for ICE and CBP records on policies surrounding IMSI catchers, the number of times the surveillance tools were used in each field office, and when they were used on behalf of outside agencies.

In that request, the ACLU also wanted ICE to disclose how often data obtained with IMSI catchers had been used as evidence in immigration court proceedings, and details about search warrants related to the cell site simulators.

The civil liberties organization wants to know how ICE is ensuring that people's civil liberties are protected while the border agency is using IMSI catchers, and has requested documents showing what rules and regulations are in place while the devices are being used.

In April, after a separate lawsuit turned up evidence regarding warrantless border searches of electronic devices, the ACLU learned through a public records request that Homeland Security had given agents free rein over thousands of devices.