CHICAGO — Over 700 flights have been grounded at Chicago’s airports on Monday, as travelers face challenges from a mix of federal government shutdown impacts and an overnight snowfall.

The combination of air traffic controller shortages and winter weather conditions resulted in delays of up to four hours at Chicago O’Hare International Airport. The Federal Aviation Administration has issued warnings that staffing issues could lead to disruptions in cities such as Philadelphia, Nashville, and Atlanta.

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According to the FAA’s website, O’Hare is currently experiencing a ground delay. As of 6:16 p.m., the FlyChicago website reports that 618 flights have been canceled at O’Hare, with delays averaging 54 minutes.

At Chicago Midway International Airport, 134 flights have been called off, with average delays of about 23 minutes, as indicated by the FlyChicago site.

The scene at O’Hare this week starkly contrasts with last week’s. Security lines have grown longer, and the tension is palpable as passengers anxiously monitor the flight information boards for updates on their travel plans.

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. 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.

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’HareandMidway, 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 was nearing a vote to end the shutdown although it would still need 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.