Senators expressed concern on Wednesday that without proper restrictions, police and private groups could use drones to invade the privacy of people in the United States.

Drones are cheaper to build and fly than helicopters, making them a cost-effective option for police departments looking to gain a bird’s eye view of a scene. Commercial drones are currently illegal, but the Federal Aviation Administration (FAA) is working on rules to grant licenses to private groups by 2015.

The FAA has predicted that by the end of the decade, 30,000 commercial and government drones could be flying in U.S. skies.

That’s a frightening prospect for lawmakers who fear the drone fleet will be used to peer into people’s private lives.