The American Civil Liberties Union of Northern California has sued the Transportation Security Administration, alleging that the agency has improperly withheld documents and other materials that would shed light on warrantless searches of digital devices at airports prior to purely domestic flights.

This lawsuit, which is meant to compel the TSA to fully respond to a Freedom of Information Act request, is related to another lawsuit (Alasaad v. Duke) brought by the ACLU to better understand such searches that happen when Americans return home from abroad.

"The federal government’s policies on searching the phones, laptops, and tablets of domestic air passengers remain shrouded in secrecy," said Vasudha Talla, staff attorney with the ACLU Foundation of Northern California, in a Monday statement.

Specifically, the ACLU of Northern California "seeks records related to policies, procedures, or protocols regarding the search of passengers’ electronic devices; equipment used to search, examine, or extract data from passengers’ devices; and training of the officers conducting the screenings and searches of electronic devices."

The advocacy group filed a FOIA request on December 20, 2017, but TSA provided no records.

"TSA is searching the electronic devices of domestic passengers, but without offering any reason for the search," Talla continued. "We don’t know why the government is singling out some passengers, and we don’t know what exactly TSA is searching on the devices. Our phones and laptops contain very personal information, and the federal government should not be digging through our digital data without a warrant."

The TSA did not respond to Ars’ request late Monday evening for comment.

Matt Leas, a TSA spokesman, declined to comment on the lawsuit to The Guardian, which first reported the lawsuit. "TSA does not search the contents of electronic devices," Leas told the British newspaper.