The FAA estimated 3.6 million hobbyist drones will be in the air by 2021.
The U.S. military branches are free to shoot down or otherwise remove unauthorized drones flying too close to military bases, according to newly declassified Pentagon guidelines.
The rules, which will let military personnel disable, track, destroy, or seize errant drones, came to light because they were declassified Friday so that the various branches of the military can communicate them to local authorities. The rules apply to both private and commercial drones.
Increased use of drones raises concerns about the security and safety of military installations, Pentagon spokesman Jeff Davis told reporters on Monday, according to CNN.
In March, the FAA estimated that some 3.6 million hobbyist drones will be in the air by 2021. And that doesn’t count the commercial drones that companies like Amazon amzn , Facebook fb , and Google googl hope to use to deliver products or Internet access to underserved areas.
It has been illegal to fly drones within 400 feet of the 133 U.S military bases since April. At that time, the FAA and U.S. Defense Department said they agreed to restrict drone use within the boundaries of these facilities—the first time the FAA implemented airspace restrictions specifically for drones and not other aircraft.
Get Data Sheet, Fortune’s technology newsletter.
Drone operators who violate that law could face to fines and possible criminal charges. Specifics on exactly how the military would track or disable drones were not provided.