The air traffic control tower at Chicago's Midway International Airport was closed Tuesday after "several" technicians there tested positive for coronavirus, the Federal Aviation Administration said.
The airport is still open but is operating at a reduced rate, according to the agency.
"The air traffic control tower at Midway Airport is temporarily closing while we ensure a safe work environment for air traffic controllers and technicians," the FAA said in a statement.
The agency said it had backup facilities in operation to help the airport continue operating.
Aviation has been at the epicenter of the coronavirus crisis as airlines and related industries reel from a sharp drop-off in demand as travelers stay home and bookings tumble.
"The FAA continues to maintain close contact with airports, airlines and other stakeholders during this situation," it said.
The National Air Traffic Controllers Association, the union that represents the about 20,000 air traffic controllers, engineers and other aviation-safety workers, said all aviation safety workers at Midway should be immediately tested for the disease, or COVID-19.
NATCA "is adamant that the testing must occur immediately and is hopeful there will be no additional COVID-19 infections," it said. "We are encouraged that the FAA is pursuing the rapid testing of all personnel at MDW Tower."