CEOs of major U.S. airlines sounded the alarm on Monday when AT&T and Verizon rolled out their new 5G service in less than 36 hours, sparking a potentially “catastrophic” aviation crisis.

The airlines warned that the new C-Band 5G service set to launch on Wednesday, could render a significant number of widebody aircraft unusable, “could potentially strand tens of thousands of Americans overseas” and cause “chaos” for U.S. flights.

Similarly, the Federal Aviation Administration (FAA) has warned that any interference could affect sensitive airplane instruments like altimeters and potentially hamper low-visibility operations.

On Monday, many airlines were considering cancelling some international flights scheduled to arrive in the U.S. on Wednesday.

“Unless our major hubs are cleared to fly, the vast majority of the travelling and shipping public will essentially be grounded,” the CEOs of American Airlines, Delta Air Lines, United Airlines, Southwest Airlines and others wrote in a published letter.

The letter, which was also signed by UPS Airlines, Alaska Air, Atlas Air, JetBlue Airways and FedEx Express, called for urgent action on the matter.

The airlines are calling for “5G be implemented everywhere in the country except within the approximate 2 miles (3.2 km) of airport runways” at some major airports.

The letter was sent to White House National Economic Council director Brian Deese, Transportation Secretary Pete Buttigieg, FAA Administrator Steve Dickson and Federal Communications Commission (FCC) Chairwoman Jessica Rosenworcel.

Verizon and AT&T did not comment on the matter, with both carriers previously arguing that C-Band 5G has been successfully deployed in about 40 other countries without disrupting air traffic.

On Sunday, the FAA announced that it has cleared an estimated 45% of the U.S. commercial airplane fleet to conduct low-visibility landings at airports where 5G C-band and further permits will be issued by the agency through Wednesday.