The chief executives of major airlines in America Monday sent a letter to the White House warning of a potential “catastrophic” aviation crisis on Wednesday when AT&T and Verizon are scheduled to switch-on new 5G services.

The CEOs reportedly said the 5G deployment “could potentially strand tens of thousands of Americans overseas.”

“Unless our major hubs are cleared to fly, the vast majority of the traveling and shipping public will essentially be grounded,” the leaders of American Airlines, Delta Air Lines, United Airlines, Southwest Airlines and others wrote in a letter, according to Reuters. “This means that on a day like yesterday, more than 1,100 flights and 100,000 passengers would be subjected to cancellations, diversions or delays.”

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