Flights across the country were suddenly grounded, delayed, or canceled on Friday after the government shutdown struck at least two key aviation command centers on the East Coast, leaving them understaffed to handle operations at full capacity.

Planes were temporarily prohibited from landing at New York’s LaGuardia airport, according to the Federal Aviation Administration, and delays built up at airports including Atlanta Hartsfield-Jackson Atlanta International Airport, Orlando International Airport, Chicago O’Hare International Airport, and Philadelphia International Airport.

“We have experienced a slight increase in sick leave at two facilities. We’ve mitigated the impact by augmenting staffing, rerouting traffic, and increasing spacing between aircraft when needed,” a spokesman for the FAA told The Daily Beast.

Four air-traffic controllers told The Daily Beast the facilities are Washington Air Route Traffic Control Center in Leesburg, Virginia and the Jacksonville Air Route Traffic Control Center. The two centers together monitor the airspace and organize flights along the eastern seaboard from Florida to New York. The controllers requested anonymity to speak freely.

“Washington, D.C. is currently in massive flow,” an air-traffic controller at Reagan Washington National Airport said. “Which means we will have one or two airplanes leave every 30 minutes and that would be an extreme flow so planes are not going to be moving for a while.”

But the delayed departures will cease if air-traffic controllers continue to call out all together.

“Three people are needed in each tower cover a midnight shift. If two were to not show up, they have to close down that tower. If enough towers are closed down, a center has to close down,” the D.C. controller explained. “There are 12 centers that control airspace. If one center closes downs, airports have to shut down completely.”

Monroe Regional Airport in Louisiana became the first airport Friday to cancel flights entirely due to shutdown shortages. It canceled both a Dallas-bound flight and an Atlanta-bound flight after not enough TSA workers showed up to open the security checkpoint. Slate reports that the checkpoint is normally staffed by ten people, but only two showed up to work Friday. The missing workers were eventually replaced by employees of nearby airports, and the checkpoint was up and running hours later.

Many passengers flying out of LaGuardia came prepared for long security lines and delays, citing horror stories from the last month.

“We were already coming early for our flight because we have heard some horror stories of people missing their flights and having to wait in line for hours. We even brought snacks,” said Ron Everson, a 52-year-old flying from New York to Arizona with his wife. “On the cab over here we saw that air traffic controllers were not coming in and that flights were grounded.”

Everson, who arrived four hours early for his flight, applauded the air traffic controllers for taking a stand despite the effects on his travel.

“All I have to say is good for fucking them. I don’t mind waiting.”

The ripple effect didn’t garner a positive reaction from many other air travelers, however.

“There may not be a long security line right now but that doesn’t matter if I have to sit on a plane forever,” said Lindsey Harold, who was traveling to Los Angeles for business. “This is extremely dangerous and they need to get back to work. I empathize but I also need them to do their job.”

About an hour after it was first imposed, the ground stop at LaGuardia was lifted, leaving travelers with an average delay of about 86 minutes, Yahoo News’ Ethan Klapper reported on Twitter.

Unlike TSA workers, who in recent weeks have called out sick en masse to protest the government shutdown, air-traffic control staff previously said that they would not intentionally call out sick in order to ensure flight safety.

But on Friday, after missing a second paycheck as the government shutdown nears its fifth week, some air-traffic controllers told The Daily Beast that they are finally fed up.

“After yesterday, we feel horrible,” an air-traffic controller at D.C.’s Ronald Reagan Washington National Airport told The Daily Beast, referencing the Senate voting down two bills that could have ended the shutdown. “If the government can’t fight for us, we are done acting in the best interest of this country. We are overworked and not getting paid.”

Over the past month, air-traffic controllers and other airport personnel have reportedly picked up side jobs to supplement their income, such as driving Uber or Lyft.

“It’s not going well,” Nick Daniels, an air-traffic control specialist with the FAA said. “Today was another look at no hope as our $0.00 paychecks turned up one again for our 160+ hours of work.”

The shutdown is scheduled to end on Friday after Trump agreed to sign legislation that will fund the government for three more weeks.

“Air-traffic controllers really put themselves on the line today but taking a stand and we are only puts a Band-Aid to the problem of us being held hostage in another three weeks,” a controller for Puerto Rico’s Luis Muñoz Marín International Airport said. “Today what we did worked and if it worked today we will continue to not come in three weeks until the government is open for the rest of the year. But we are still very happy.”

Trump previously signed a measure that would give backpay to federal workers when the government reopens, though it’s unclear how soon they will be paid.

“All I can say is I better get my money before they shutdown the government again,” a TSA agent at LaGuardia Airport said. “Regardless, I am happy this nightmare is finally over.”