By midmorning in the eastern U.S., airlines has scrubbed more than 1,000 flights after canceling more than 1,700 on Thursday, according to tracking service FlightAware.
LaGuardia Airport and Newark Liberty International Airport were among those with the highest number of cancellations, along with Charlotte, North Carolina, and Reagan Washington National outside Washington, D.C.
So far in June, more than 2.2 million travelers a day on average have gone through security checkpoints at U.S. airports. That's down 13% from the same period before the pandemic.
Airlines cancelled more than 1,600 flights Thursday, including a third of flights at LaGuardia and a quarter at Newark.
The cancellations came less than three weeks after airlines kicked off the summer travel season by canceling about 2,800 flights in a five-day stretch around the Memorial Day holiday weekend.
Now, Transportation Secretary Pete Buttigieg is putting the airline industry on notice.
He pressed airlines over their ability to reliably operate their July 4 holiday flight schedules and asked them to improve customer experience in a meeting with airline executives and industry insiders, a source familiar with the meeting told ABC News.
Buttigieg also said that the FAA would continue to keep air traffic smooth and on schedule after criticism from some industry groups that FAA ground stops and delays caused by weather resulted in many of the delays over the Memorial Day weekend.
"I let them know that this is a moment when we are really counting on them to deliver reliably for the traveling public," Buttigieg told NBC News.
During the meeting, which took place by videoconference, Buttigieg asked the CEOs to describe steps they are taking to operate smoothly over the July 4 holiday and the rest of the summer.
Buttigieg also pushed airlines to examine whether they can handle the schedules that they have published, and to improve customer service.
The head of trade group Airlines for America, Nicholas Calio, said in a statement that industry officials appreciated the chance to talk with Buttigieg and "discuss our shared commitment to prioritizing the safety and security of all travelers."
Airlines are struggling with shortages of workers, especially pilots, that are hurting their ability to operate all their planned flights. Pilot unions at Delta, American and Southwest have said their airlines were too slow to replace pilots who retired or took leaves of absence during the early part of the pandemic.
Two Senate Democrats said this month that the holiday weekend performance "raises questions about airline decision-making." Richard Blumenthal of Connecticut and Edward Markey of Massachusetts said delays and cancellations "are occurring so frequently that they are becoming an almost-expected part of travel."
The airlines blame bad weather and the FAA, an arm of the Transportation Department that manages the nation's airspace. In a letter to the senators, Calio ticked off a long list of FAA delays and staffing problems over the holiday weekend.
The airlines have jousted with the FAA this spring over delays in Florida, where air travel recovered more quickly than in many other parts of the country. After meeting with airline representatives in May, the FAA agreed to increase staffing at an air-traffic control center near Jacksonville and make other changes.
Concern about flight problems comes as the number of air travelers in the U.S. pushes above 2.2 million a day. That is still about 300,000 fewer per day than in mid-June 2019, but crowds will grow over the next several weeks and almost certainly break the pandemic-era record set on the Sunday after Thanksgiving last year.
Bottlenecks could pop up at gateway airports where travelers enter the United States. Last weekend, the Biden administration dropped a 16-month requirement that people test negative for COVID-19 before boarding a flight to the U.S. That decision is expected to boost international travel - United Airlines said Monday that it saw an immediate increase in searches for overseas flights.
Another threat: The FAA is urging airlines to quickly upgrade equipment that might be vulnerable to radio interference from new wireless service. The agency's acting administrator, Billy Nolen, told airlines Wednesday that Verizon and AT&T plan to turn on hundreds of 5G C-band transmitters near airports on July 5.
Dire forecasts of fallout from the wireless companies' initial C-band service failed to come true early this year. Still, Nolen said FAA can't promise that there won't be problems with some planes. He said industry officials have found a way to retrofit many planes with problematic gear by the end of the year and others in 2023.
Shares of the largest six U.S. airlines dropped between 6% and 9% on Thursday, as jitters about the economy sent the broader market tumbling.
(The Associated Press contributed to this report)
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