Wireless operators are under increasing pressure to hand over private information about their subscribers to law enforcement agencies, raising concerns about consumer privacy.

Congressman Ed Markey released data on Monday stating that federal, state and local officials placed more than 1.3 million requests for cell phone records last year.

“Law enforcement agencies are looking for a needle, but what are they doing with the haystack?" the Massachusetts Democrat said in a statement. Markey is co-chair of the bi-partisan Congressional privacy caucus. "We need to know how law enforcement differentiates between records of innocent people and those that are subjects of investigation, as well as how it handles, administers and disposes of this information.”

The report is the first-ever data collected on the information requests, as there is no comprehensive reporting required on the practice.

Markey asked for reports from U.S. Cellular, Sprint, T-Mobile USA, Leap Wireless International, MetroPCS, Verizon, AT&T, C Spire Wireless and Tracfone. In separate responses, the companies all said they only provided private customer data when authorities followed the required legal process.

Verizon said information requests from law enforcement have risen 15 percent each year for the past five years. It has a dedicated team of 70 staffers who work around the clock to review the requests.

T-Mobile said it has witnessed annual increases in the requests of between 12 percent and 16 percent.

AT&T said it employs more than 100 full-time workers to meet demands for information. Like Verizon's employees, AT&T's team also works 24 hours a day, seven days a week, to stay in compliance with federal regulations. Though the number of information requests it fills each year may seem high, AT&T pointed out that the information provided affected just one-quarter of 1 percent of its wireless customer base.

Sprint has 36 analysts to review court orders for the installation of wiretaps and the tracing of devices, plus an additional 175 analysts to respond to subpoenas and court orders for subscriber information.