Mobile privacy safeguards should also extend to third party application developers, two lawmakers said after reviewing the practices of four major U.S. wireless carriers.

Representatives Edward Markey and Joe Barton, co-chairs of the House Bi-Partisan Privacy Caucus, on Thursday released letters they received from Verizon Wireless, AT&T Inc, Sprint Nextel and T-Mobile in response to their inquiries last month about the collection, use and storage of location data.

"After thoroughly reviewing the responses from the wireless carriers, I am left with a feeling of uneasiness and uncertainty," Barton said in a statement.

Verizon Wireless is a joint venture of Verizon Communications and Vodafone Group Plc, while AT&T has bid $39 billion to buy T-Mobile from Deutsche Telekom AG.

While receiving customer consent before accessing location data was common practice among the wireless carriers, Barton said there was a disconnect for third-party applications.

"Third-party developers can access the location of customers any time they want," Barton said. "They shouldn't have free reign over your location data and personally identifiable information."

Markey echoed this sentiment, saying consumer privacy protections must apply "across the entire wireless ecosystem - from wireless carriers, to mobile handset makers, to application developers."

Markey and Barton grew concerned about location tracking after media reports found that Deutsche Telekom tracked the exact coordinates of a German politician using its service over a six-month period.

The letters revealed varying use across the wireless carriers of encryption and other security technologies to protect customers' personal data. The data was also stored for varying periods of time by the companies.

To curb security breaches that can lead to identity theft, Markey said sensitive data on mobile phones should only be readable by those with a legitimate need to access it, and the data should be stored for the shortest periods necessary.

The issue took the spotlight recently after reports suggested Apple Inc's iPhone was monitoring the whereabouts of its users.

Apple has denied tracking its customers, but said it would release a software update to cut the size of the wireless hotspot location database stored on its iPhones, and stop backing up that information.

Senate Commerce Committee Chairman Jay Rockefeller will hold a hearing in May on consumer protection and privacy in the mobile marketplace. Senator Al Franken said on Thursday both Google and Apple would attend his May 10 hearing, the first by the new Senate judiciary subcommittee on privacy, technology and the law.