Air traffic controllers will miss their paychecks Tuesday because of the ongoing government shutdown, raising concerns that mounting financial stress could take a toll on the already understaffed employees who guide thousands of flights each day.

Flight delays are becoming more common across the country as more controllers call out sick because the Federal Aviation Administration was already so short on controllers before the shutdown.

Transportation Secretary Sean Duffy and the president of the National Air Traffic Controllers Association Nick Daniels have continued to emphasize the pressure that controllers are feeling. They say the problems are likely to only get worse the longer the shutdown continues.

Not only are controllers worrying about how to pay for their mortgages and groceries, but Daniels said some of them are also grappling with how to pay for the medicine needed to keep their children alive. Duffy said he heard from one controller who had to tell his daughter she couldn’t join the traveling volleyball team she had earned a spot on because he couldn’t afford the cost during the shutdown.

“Air traffic controllers have to have 100% of focus 100% of the time,” Daniels said Tuesday at a news conference alongside Duffy at LaGuardia Airport in New York. “And I’m watching air traffic controllers going to work. I’m getting the stories. They’re worried about paying for medicine for their daughter. I got a message from a controller that said, ‘I’m running out of money. And if she doesn’t get the medicine she needs, she dies. That’s the end.’”

The FAA restricts the number of flights landing and taking off at an airport anytime there is a shortage of controllers to ensure safety. Most of the time that has meant delays — sometimes hours long — at airports like New Jersey’s Newark Liberty International Airport or Burbank airport in California. But over the weekend, Los Angeles International Airport actually had to stop all flights for nearly two hours.

Controllers are planning to assemble outside at least 17 airports nationwide Tuesday to hand out leaflets urging an end to the shutdown as soon as possible. Worrying about how to pay their bills is driving some to take second jobs to make ends meet.

The number of controllers calling in sick has increased during the shutdown both because of their frustration with the situation and because controllers need the time off to work second jobs instead of continuing to work six days a week like many of them routinely do. Duffy has said that controllers could be fired if they abuse their sick time, but the vast majority of them have continued to show up for work every day.

Air traffic controller Joe Segretto, who works at a regional radar facility that directs planes in and out of airports in the New York area, said morale is suffering as controllers worry more about money.

“The pressure is real,” Segretto said. “We have people trying to keep these airplanes safe. We have trainees — that are trying to learn a new job that is very fast-paced, very stressful, very complex — now having to worry about how they’re going to pay bills.”

Duffy said the shutdown is also making it harder for the government to reduce the longstanding shortage of about 3,000 controllers. He said that some students have dropped out of the air traffic controller academy in Oklahoma City, and younger controllers who are still training to do the job might abandon the career because they can’t afford to go without pay.

“This shutdown is making it harder for me to accomplish those goals,” Duffy said.

The longer the shutdown continues, pressure will continue to build on Congress to reach an agreement to reopen the government. During the 35-day shutdown in President Donald Trump’s first term the disruptions to flights across the country contributed to the end of that disruption. But so far, Democrats and Republicans have shown little sign of reaching a deal to fund the government.