https://www.cbsnews.com/news/airspace-closure-followed-spat-over-drone-related-tests-and-party-balloon-shoot-down-sources-say/
"The anti-drone technology was launched near the southern border to shoot down what appeared to be foreign drones. The flying material turned out to be a party balloon, sources said. One balloon was shot down, several sources said.
critical bulletin issued to pilots and airlines not to fly below 18,000 feet was initially set for 10 days, a duration for a full grounding not used since the 9/11 terror attacks. The FAA notice warned violators risked being shot down.."