Airlines canceled more than 1,400 flights in the U.S. on Thursday, one of the worst days yet for travel as the peak summer vacation season heats up.

At LaGuardia Airport in New York, more than one-third of all flights were scrubbed, and more than one-fourth of flights were dropped at nearby Newark Liberty airport in New Jersey, according to tracking service FlightAware.

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.

And they happened as airline CEOs held a virtual meeting with Transportation Secretary Pete Buttigieg — a sign of the Biden administration’s concern about the prospect of snarled airports and unhappy travelers this summer.

“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, according to a person familiar with the call but not authorized to discuss it publicly.

Buttigieg also pushed airlines to examine whether they can handle the schedules that they have published, and to improve customer service, the person said.

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.

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