ap photo Airport staff looks at a tag on a pile of lost suitcases near the baggage carousel at Midway Airport, Tuesday, after Southwest Airlines flights were cancelled and delayed during a winter storm. Problems at Southwest Airlines appeared to snowball after the worst of the storm passed. It cancelled more than 70 percent of its flights Monday, more than 60 percent on Tuesday.

DALLAS — Southwest Airlines scrubbed thousands of flights again Tuesday in the aftermath of the massive winter storm that wrecked Christmas travel plans across the U.S., and the federal government said it would investigate why the company lagged so far behind other carriers.

A day after most U.S. airlines had recovered from the storm, Southwest called off about 2,600 more flights on the East Coast by late afternoon. Those flights accounted for more than 80% of the 3,000 trips that got canceled nationwide Tuesday, according to tracking service FlightAware.

And the chaos seemed certain to continue. The airline also scrubbed 2,500 flights for Wednesday and nearly 1,400 for Thursday as it tried to restore order to its mangled schedule.

At airports with major Southwest operations, customers stood in long lines hoping to find a seat on another flight. They described waiting hours on hold for help, only to be cut off. Some tried to rent cars to get to their destinations sooner. Others found spots to sleep on the floor. Luggage piled up in huge heaps.

Conrad Stoll, a 66-year-old retired construction worker in Missouri, planned to fly from Kansas City to Los Angeles for his father’s 90th birthday party until his Southwest flight was canceled early Tuesday. He said he won’t get to see his 88-year-old mother either.

“I went there in 2019, and she looked at me and said, ‘I’m not going to see you again.'” Stoll said. “My sister has been taking care of them, and she’s just like, ‘They’re really losing it really quick.'”

Stoll hopes to get another chance to see his parents in the spring, when the weather is warmer.

The Dallas-based airline had little new to say about its woes. The company did not offer any updates Tuesday afternoon. Its website gave customers the chance to change or cancel flights while warning that the phone system was “very busy due to high demand.”

The problems began over the weekend and snowballed Monday, when Southwest called off more than 70% of its flights.

That was after the worst of the storm had passed. The airline said many pilots and flight attendants were out of position to work their flights. Leaders of unions representing Southwest pilots and flight attendants blamed antiquated crew-scheduling software and criticized company management.

Casey Murray, president of the Southwest Airlines Pilots Association, said the airline failed to fix problems that caused a similar meltdown in October 2021.

“There is a lot of frustration because this is so preventable,” Murray said. “The airline cannot connect crews to airplanes. The airline didn’t even know where pilots were at.”

Murray said managers resorted this week to asking pilots at some airports to report to a central location, where they wrote down the names of pilots who were present and forwarded the lists to headquarters.

Lyn Montgomery, president of the Transport Workers Union representing Southwest flight attendants, was scheduled to talk Tuesday with Transportation Secretary Pete Buttigieg, who has criticized airlines for previous disruptions and is now taking an interest in Southwest’s woes.

“I’m taking it to the highest level — that is how done we are,” said the frustrated Montgomery. “This is a very catastrophic event.”

Buttigieg’s office confirmed that he planned to speak with Montgomery, but declined to comment further on the mess at Southwest.

Late Monday, the Transportation Department tweeted that it would examine “Southwest’s unacceptable rate of cancellations” and whether the airline was meeting its legal obligations to stranded customers.

In Congress, the Senate Commerce Committee also promised an investigation. Two Senate Democrats called on Southwest to provide “significant” compensation for stranded travelers, saying that the airline has the money because it plans to pay $428 million in dividends next month.

Southwest spokesman Jay McVay said the cancellations grew as storm systems moved across the country, leaving flight crews and planes out of place.

“So we’ve been chasing our tails, trying to catch up and get back to normal safely, which is our number one priority, as quickly as we could,” he told a news conference late Monday in Houston.

Bryce Burger and his family were supposed to be on a cruise to Mexico departing from San Diego on Dec. 24, but their flight from Denver was canceled without warning. The flight was rebooked through Burbank, California, but that flight was canceled while they sat at the gate.