“CBP is responsible for ensuring compliance with customs, immigration, and other Federal laws at the border. To that end, officers may examine documents, books, pamphlets, and other printed material, as well as computers, disks, hard drives, and other electronic or digital storage devices,” state the guidelines published on July 18.

The document claims these examinations are part of the CBP's long-standing practice and are essential to uncovering vital law enforcement information.

“For example, examinations of documents and electronic devices are a crucial tool for detecting information concerning terrorism, narcotics smuggling, and other national security matters; alien admissibility; contraband including child pornography, monetary instruments, and information in violation of copyright or trademark laws; and evidence of embargo violations or other import or export control laws.”

A statement from the free speech organisation the Center for Democracy and Technology (CDT) said the rules applied even when officials have no suspicion that a device contains evidence of a crime.

“Devices can be taken from travellers, removed to a remote location, examined by officials unknown to the travelers, and returned days, weeks, or even months later,” the CDT statement said.