WATCH: Duffy and Air Traffic Controllers Union President hold briefing on impact of federal shutdown

The ongoing government shutdown continues to disrupt flights at times and put pressure on air traffic controllers who work without pay.

Watch Transport Minister Sean Duffy’s news briefing in the video player above.

Flights were delayed Thursday at LaGuardia Airport in New York, Newark Airport in New Jersey and Reagan National Airport in Washington due to a shortage of air traffic controllers. The number of flights delayed for any reason nationwide rose to 6,158 on Thursday from hovering around 4,000 the previous day of the week, according to FlightAware.com. On Friday afternoon, Houston Airport also reported average delays of about a half-hour due to staffing issues, and the Federal Aviation Administration warned of potential issues at airports in the New York, Dallas and Phoenix area.

He watches: Airports are facing delays as closures exacerbate staffing problems in air traffic control

Many FAA facilities are so short on controllers that even just a few absences can cause disruptions, and Transportation Secretary Sean Duffy said more air traffic controllers have begun calling in sick since the shutdown began. Early in the lockdown period, there were a number of disruptions at airports across the country, but over the past two weeks, there haven’t been many problems.

The disruptions and delays will get worse next week after payday arrives on Tuesday and “their paycheck will be a big zero,” Duffy said. He said supervisors tell him they are worried about how to pay their bills and are frustrated by the closure.

“I think the level of pressure that our controllers are under now is unacceptable,” he said at a news conference on Friday at the Philadelphia airport.

Duffy said the closure has real consequences, with some students at the Control Academy already deciding to give up the profession because they don’t want to work a job they won’t get paid for.

This will make it difficult for the FAA to hire enough controllers to eliminate the shortage, because training takes years. He said the government was only a week or two away from running out of money to pay the salaries of students at the academy.

“We’re getting word now from our academy in Oklahoma City that some of our young controllers at the academy and some of those who have earned spots in the next class of the academy are going to bail. They’re leaving,” Duffy said. “They ask themselves, why would I want to pursue a career where I can work hard and potentially not get paid for my services?”

Air Traffic Controllers Association President Nick Daniels joined Duffy. He said some controllers have already taken on second jobs delivering for DoorDash or driving for Uber to earn cash to help them pay their bills while the shutdown continues.

He watches: Federal workers are set to lose their full pay as the government shutdown continues

“As this shutdown continues, and air traffic controllers are not getting paid for the vital work they do day in and day out, it creates unnecessary distraction,” Daniels said. “They can’t focus 100% on their jobs, which makes this system less safe. Every day that this shutdown continues, we will be less safe tomorrow than today.”

Airlines and airports across the country have begun purchasing meals for observers and helping them connect with food banks and other services to help them get through the shutdown.

The biggest concern is for new proctors who may be making less than $50,000, but even experienced proctors who make more than six figures while working six days a week may live paycheck to paycheck without much support in their budgets. Daniels said it’s not fair that probationers face impossible choices about whether to pay for rent, childcare or groceries.

Air traffic controllers who abuse their sick time during the shutdown could be fired, Duffy said.

Republicans and Democrats were unable to reach an agreement to end the shutdown that began on October 1. Airlines and major unions across the industry have urged Congress to reach a deal to end the shutdown.

Airline Pilots Association President Capt. Jason Ambrosie said in a letter to his members that he is concerned about air traffic controllers and other federal employees.

“The safety of millions of passengers and tens of thousands of tons of cargo is in the hands of these workers. Worrying about how to make their mortgage payments or pay for daycare is additional stress they don’t need,” Ambrosie said.

Rep. Sam Graves, chairman of the House Transportation and Infrastructure Committee, urged Democrats to support the GOP bill to fund the government to help ensure the safety of the flying public.

“Our aviation system has operated safely throughout the shutdown, but it places incredible and unnecessary stress on the system, on our air traffic controllers, flight crews, and many other aviation professionals,” said Graves, a Republican from Missouri.