The chairman and five other Republicans of the House Homeland Security Committee on Tuesday requested a classified briefing by North American Aerospace Defense Command (NORAD) and the Department of Homeland Security on the recent violation of U.S. airspace by a high-altitude Chinese surveillance balloon that was eventually shot down in the Atlantic Ocean near the coast of South Carolina.

The congressmen said the balloon “posed a serious threat to the American homeland” as an intelligence platform and are concerned that previous incursions by Chinese surveillance balloons went undetected.

“As we learned on that fateful day in September 2001, airspace control and defense is a critical pilar in security our nation against foreign threats,” says the letter, which was signed by Chairman Mark Green (Tenn.), August Pfluger (Texas), Dan Bishop (N.C.), Tony Gonzalez (Texas), Anthony D’Esposito (N.Y.), and Elijah Crane (Ariz.). The letter was sent to Air Force Gen. Glen VanHerck, who is also commander of U.S. Northern Command, and Homeland Security Secretary Alejandro Mayorkas.

VanHerck and others testified last week to the Senate Appropriations Defense Subcommittee about the balloon incident in both an unclassified hearing as well as a follow-up classified briefing for all members of Congress. There was also a classified briefing for senators on Tuesday.

Green and his colleagues also said it was “unacceptable” for Congress to learn about the incidents through news reports and want the briefers to “discuss with us all of the capabilities that thee aircrafts possess that pose a threat to the homeland.” They want the committee to be briefed by March 10.

Since the Chinese balloon incident in late January and early February, U.S. fighter aircraft have shot down three additional, but smaller, objects flying north of Alaska, in Canada and above Lake Huron. These aircraft have not been identified but were also slow moving and were at altitudes between 20,000 and 40,000 feet, well below the level flown by the Chinese balloon, which was shot down at around 65,000 feet.