The American Civil Liberties Union on Monday warned that legislation approved by Congress could severely undermine Americans' privacy.

On Monday, the Senate passed H.R. 658, a bill that would make it easier for law enforcement agencies to obtain and use unmanned aerial vehicles. The bill was passed by the House on Friday.

"Unfortunately, nothing in the bill would address the very serious privacy issues raised by drone aircraft," Jay Stanley of the ACLU said. "This bill would push the nation willy-nilly toward an era of aerial surveillance without any steps to protect the traditional privacy that Americans have always enjoyed and expected."

The Federal Aviation Administration has restrained the domestic use of drones out of concern for the safety of U.S. airspace. The use of drones has been mostly limited to the U.S.-Mexico border and in war-zones outside the country.

But provisions in H.R. 658 would require the FAA to speed up the process by which it authorizes government agencies to operate drones. The bill would also require the agency to allow agencies to operate any drone weighing 4.4 pounds or less as long as it was operated within line of sight, during the day and below 400 feet in altitude.

There are hundreds of different models of drones, from large fixed-wing aircraft to a tiny drone called the Nano Hummingbird. The drones employ a wide range of surveillance technology as well, including high-power zoom lenses, infrared and ultraviolet imaging, see-through imaging and video analytics.

The U.S. Supreme Court ruled in the 1980s that the Fourth Amendment did not categorically prohibit warrantless aerial surveillance of private property. The cost of purchasing, operating and maintaining aircraft imposed a natural limit on aerial surveillance.

With the advent of drones, however, the ACLU doesn't see law enforcement agencies being held back by the costs.

"The bottom line is: domestic drones are potentially extremely powerful surveillance tools, and that power — like all government power — needs to be subject to checks and balances," Stanley concluded. "We hope that Congress will carefully consider the privacy implications that this technology can lead to."