WASHINGTON — U.S. Sen. Ed Markey (D-Mass.) said he has sent letters to the major wireless carriers seeking more information related to his ongoing investigation into law enforcement requests for, and surveillance of, mobile data.

Markey asked for the number of requests for data mobile providers received from law-enforcement agencies in 2013 and 2014, as well as whether those requests came via warrant or some other standard. His inquiry was driven mainly by a report in The Wall Street Journal that federal and local law-enforcement agencies in some instances were not obtaining warrants before using tracking equipment to harvest data.  

Markey's latest request also seeks data on whether the wireless carriers had received requests for encryption keys so customer communications could be decrypted.

Letters were sent to AT&T, C Spire Wireless, Cricket Wireless, Sprint, T-Mobile USA, US Cellular and Verizon Communications. Markey wants the information by June 11.

The letters come as the Senate debates the USA Freedom Act, a bill intended to end indiscriminate bulk collection of telecom data by the National Security Agency.

The House has passed the bill, but the Senate has yet to act, and an alternative offered up by Senate Majority Leader Mitch McConnell (R-Ky.) would renew that bulk collection as part of a short-term straight renewal of provisions in the USA PATRIOT Act set to sunset at the end of the month.

“America is in the middle of an historic national debate about the legal, constitutional and privacy implications of the mass collection of our telephone information,” said Markey, a member of the Commerce Committee, which oversees communications. “Mobile-phone data can be an important tool in law enforcement efforts to protect Americans, but we cannot allow the pervasive collection of this information, especially of innocent Americans.

“As mobile phones have become 21st century wallets, personal assistants, and navigation devices — tracking each click we make and step we take — we need to know what information is being shared with law enforcement," Markey added.