The Federal Aviation Administration has carved out no-drone zones over 133 military facilities in the U.S. as the government steps up efforts to marshal what potentially could be millions of small commercial and recreational drones entering the airspace in the next few years. Drone flights from the surface to 400 feet above the facilities are prohibited as of April 14, the agency said.

The action represents the first time the FAA has instituted airspace restrictions that apply only to drones, the agency said in an April 6 announcement. It cited a federal regulation—14 CFR 99.7 Special Security Instructions—as giving it the authority. The provision, which dates to 2004, requires that “each person operating an aircraft in an ADIZ (Air Defense Identification Zone) or defense area must…comply with special security instructions issued by the Administrator in the interest of national security, pursuant to agreement between the FAA and the Department of Defense, or between the FAA and a U.S. federal security or intelligence agency.”

In its latest aerospace forecast released in March, the FAA predicted that the fleet of small drones operated by hobbyists could more than triple in size from an estimated 1.1 million vehicles last year to more than 3.5 million units by 2021. The fleet of commercial drones could grow from 42,000 vehicles in 2016 to somewhere between 442,000 and 1.6 million. The agency said it provided high and low ranges to reflect “uncertainty about the public’s continued adoption of this new technology.”

Under an application process outlined in short-term reauthorization legislation that became law last July, the FAA said it is considering additional requests from federal security and intelligence agencies to restrict or prohibit flights of small unmanned aircraft systems (UAS) “in close proximity to a fixed-site facility.”

The agency issued a Notice to Airmen (Notam) explaining the airspace restrictions and provided a link to an online interactive map with UAS-specific information that depicts flight-restricted areas as red polygons. It has also provided a link to the restrictions on its “B4UFLY” mobile application.

But Jonathan Rupprecht, an aviation attorney and flight instructor based in West Palm Beach, Florida, found the FAA’s notification effort lacking for restrictions that carry the possibility of civil or criminal penalties for commercial drone pilots operating under the FAA’s Part 107 regulation and hobbyists flying under Part 101. Hobbyists at present must register with the FAA. Part 101 provides guidelines for safely operating model aircraft and drones, but gives the FAA latitude to decide if a drone is operated “in a manner that endangers the safety” of the National Airspace System.

“I didn’t see any notice in the Federal Register, Rupprecht said of the military-site airspace restrictions. “The FAA kind of plays fast and loose with the law; it just kind of barks really loud and hopes people obey. How do people know about a Notam if you are not in the aviation community? Is the Notam proper notice? If you fly into these zones, watch out. Practicality-wise, just don’t fly there dude—nobody’s going to help you out for free.”

Since 2009, the FAA has participated on a senior-level Unmanned Aircraft Systems Executive Committee (UAS ExCom) with the Department of Defense (DOD), the Department of Homeland Security and NASA. In March, the FAA announced that ExCom membership is being expanded to include the departments of Interior, Justice and Commerce. The agency could not immediately say whether the ExCom was behind the airspace restrictions announced on April 6.

The military is moving ahead with efforts to address the challenge drones present. Congress inserted language in the Fiscal Year 2017 National Defense Authorization Act that former President Barack Obama signed into law in December that allows the military to track, disrupt, seize and even destroy drones. The secretary of defense and the armed forces are empowered “to take such actions…that are necessary to mitigate the threat (as defined by the secretary of Defense, in consultation with the secretary of Transportation) that an unmanned aircraft system or unmanned aircraft poses to the safety or security of a covered facility or asset.” The legislation defines covered facilities as structures relating to the Pentagon’s nuclear deterrence, missile defense and space missions.

In March, Gen. John Hyten, commander of the U.S. Strategic Command at Offutt Air Force Base, Nebraska, informed the House Armed Services Committee in written testimony that unauthorized drone flights over Air Force and Navy installations were causing concern over the safety and security of nuclear weapons and military personnel. Both services are working on counter-UAS systems to address the intrusions, he stated.

During a Senate Armed Services Committee hearing on April 4, Sen. Deb Fischer (R-Neb.) asked Hyten if he considered those flights to be incidental activities or deliberate actions. “So far, they’ve been incidental activities,” he responded. “But the fact that they’re occurring—and if you watch what is happening overseas in the (U.S. Central Command) theater with the use of lethal UAVs and the use of UAVs for surveillance on the part of a terrorist adversary—I’m very concerned that those same kind of UAVs could be employed against our weapons storage facilities, especially the nuclear weapons storage facilities.”

Hyten added: “Just in the last week I’ve signed out guidance to my forces to give them parameters on how they should respond if they see a threat UAV or a surveillance UAV, so a young Marine at Kings Bay [Georgia] or an airman at F.E. Warren [Air Force Base] doesn’t have to worry about what should I be doing when I see that?”