Civil liberty defenders are raising alarm over the Transportation Security Administration's (TSA) increasingly common searches of domestic travelers' personal electronic devices, including laptops, tablets, and cell phones.

The TSA announced last October that it would begin using heightened procedures to screen electronics, but the details of how the policy is implemented and how agents decide which travelers can be subjected to a warrantless search of their devices remain "shrouded in secrecy," according to the American Civil Liberties Union (ACLU).

"Our phones and laptops contain very personal information, and the federal government should not be digging through our digital data without a warrant." —Vasudha Talla, ACLU

After receiving numerous complaints from Americans regarding what they say is an invasion of their privacy by the TSA, the ACLU's Northern California chapter filed suit on Monday, demanding information about TSA's procedures and protocols for searching travelers' electronics and equipment used to search or extract data from personal devices.

"TSA is searching the electronic devices of domestic passengers, but without offering any reason for the search," said Vasudha Talla, a staff attorney with the ACLU. "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 lawsuit comes three months after the ACLU filed a Freedom of Information Act (FOIA) request asking for details on the search policy, following which the TSA has "improperly withheld" the requested government documents.

"These are materials that should not be terribly difficult to track down," Talla told the Guardian, which first reported on the ACLU's suit. "We’re just not clear what they're doing and why they're doing it."

The national ACLU and Electronic Frontier Foundation has also challenged Customs and Border Protection's (CBP) practice of searching the personal electronics of people entering the U.S. at border crossings without probable cause. Thirty-thousand searches were performed by the CBP in 2017, up from 5,000 two years earlier.