A leader in cybersecurity policy is calling on Congress to investigate a flaw that makes cellular devices worldwide vulnerable to surveillance by hackers and foreign intelligence agencies, according to a letter obtained by the Washington Examiner.

“A critical component of our global mobile communications system is the architecture of protocols that directs the content of our mobile communications to their intended destination,” Rep. Ted Lieu, D-Calif., wrote in a Monday letter addressed to leaders on the House Oversight and Government Reform Committee.