While drones may serve many useful purposes, they can also enable "invasive and pervasive surveillance without adequate privacy protections," the two lawmakers wrote.

They noted that many drones are equipped to carry video cameras, infrared thermal imagers, radar and wireless network sniffers. "The surveillance power of drones is amplified when the information from onboard sensors is used in conjunction with facial recognition, behavior analysis, license plate recognition" and other systems, the letter stated.

The two lawmakers, who are co-chairmen of the Congressional Bipartisan Privacy Caucus, demanded to know what the FAA is doing to build privacy and public transparency requirements into its drone-licensing program.

The lawmakers also want to know if the public will be notified when the drones will be used, by whom and for what purpose, what data is collected and how it will be used, stored and destroyed. They also wanted to know if the FAA would require drone operators to abide by specific privacy guidelines and what those guidelines would be.

Markey and Barton asked the FAA if the agency plans on working with businesses, government, law enforcement and community groups on privacy and transparency issues as it maked rules for drone use in the U.S.