Controller shortages combined with wintry weather led to four-hour delays at Chicago O'Hare International Airport, at one point, on Monday, with the Federal Aviation Administration warning that staffing at more than a dozen towers and control centers could cause disruptions in cities including Philadelphia, Nashville and Atlanta.
There is a ground delay at O'Hare, according to the FAA website. As of 9:20 p.m., 652 flights have been canceled at O'Hare, with delays averaging 34 minutes, the city's FlyChicago website said.
There was a ground stop at the Northwest Side airport earlier Monday, the FAA website said. It has since been lifted.
At Chicago Midway International Airport, 134 flights have been canceled with delays averaging 66 minutes, according to the FlyChicago site.
The difference between last week and this week at O'Hare is noticeable. Security lines are longer, and you can feel the anxiousness of passengers near the flight information boards as they check to see the latest status of their flights.
"We had to pay $450 for a ticket to get home, because our first flight was canceled," said Anaya Ross, who was traveling to Houston. "I don't think I see myself flying anytime soon, until they get everything figured out... I'm not coming back for Thanksgiving!"
This comes as air travelers should expect worsening cancellations and delays this week even if the government shutdown ends, as the FAA moves ahead with deeper cuts to flights at 40 major U.S. airports, officials said Monday.
Day four of the flight restrictions saw airlines scrap almost 2,000 flights nationwide by Monday afternoon after cancelling 5,500 since Friday.
"We got that flight. That was delayed. And so, then, we canceled that flight, got another flight," said Barry Feuerstein, who was traveling to New Jersey. "We usually go away on the holidays. I think we're gonna take this one off."
Some air traffic controllers - unpaid for more than a month - have stopped showing up, citing the added stress and need to take second jobs.
President Donald Trump pressured controllers Monday on social media to "get back to work, NOW!!!" He said he wants a $10,000 bonus for controllers who've stayed on the job and to dock the pay of those who didn't.
The head of the controllers union said they're being used as a "political pawn" in the fight over the shutdown. Monday marked the second missed paycheck for those employees.
Darrell English, the president of AFGE Local 777, the union representing TSA officers in Illinois and Wisconsin, says the length of this shutdown has forced some officers to quit their jobs.
"If TSA officers get to that point where they continue to leave because the stressful atmosphere and not being paid and need something more stable, it's going to be a ripple effect. You can't get officers for TSA right off the street," English said.
DePaul University Aviation Expert Joe Schwieterman weighed in as disruption to air travel grows.
"Those warnings from a couple days ago are playing out today, especially O'Hare and Midway, which are leading the country in cancellations. Delays are one thing. Now, we have, you know, close to a quarter of the flights canceled. You throw into that the president's text, and it creates just a sense of disruption out there right now that people are really apprehensive," Schwieterman said.
A potential silver lining is that if the government shutdown is resolved over the next few days, Schwieterman says, the impact to holiday travel for the the Thanksgiving holiday may be minimal.
The Senate on Monday approved a spending bill to end the shutdown. Although, still needs to clear the House, and final passage could still be days away.
Transportation Secretary Sean Duffy made clear last week that flight cuts will remain until the FAA sees safety metrics improve.
Over the weekend, airlines canceled thousands of flights to comply with the order to drop 4% of flights at 40 of the nation's busiest airports. That will rise to 6% on Tuesday and 10% by week's end, the FAA says.
The Associated Press contributed to this report.