CHICAGO (CBS) — As the longest government shutdown in U.S. history moved into its 34th day on Thursday, three labor unions were warning the nation’s entire aviation security system could soon break down under the pressure.

Unions representing air traffic controllers, airline pilots, and flight attendants outlined what they called “serious safety concerns” caused by the shutdown. In all, the unions represent 130,000 federal and private employees who work at the nation’s airports.

Staffing in air traffic control facilities across the country is at a 30-year low due to the partial government shutdown, according to the unions.

The unions said their members are working overtime, including 10-hour days, and six-day work weeks at many of the nation’s busiest airports, in order to keep the system running and the flying public safe.

The National Air Traffic Controllers Association’s 20,000 members are among 800,000 federal workers who will go a second pay period without a check by tomorrow if the shutdown continues.

The unions said nearly 20 percent of air traffic controllers are eligible to retire, and many might elect to do just that if they can’t afford to keep working without a paycheck.

“When they elect to retire, the National Airspace System … will be crippled,” the unions said in a joint statement.

According to the unions, the FAA has frozen hiring and closed its training academy due to the shutdown, so it can’t fill any open positions. The unions said it takes two to four years to become an air traffic controller even if the FAA were still hiring.

“As union leaders, we find it unconscionable that aviation professionals are being asked to work without pay and in an air safety environment that is deteriorating by the day. To avoid disruption to our aviation system, we urge Congress and the White House to take all necessary steps to end this shutdown immediately,” the unions said.

TSA workers, safety inspectors, and air marshals also are among those being forced to workout pay.

Many affected workers have been calling in sick during the shutdown, and a shortage of workers has caused airports to close some security checkpoints, with many more to follow if the shutdown doesn’t end, according to the unions.

It’s unclear if any security checkpoints have been closed at O’Hare or Midway airports due to a shortage of TSA workers, but Chicago officials said wait times at O’Hare have averaged 15 minutes or less since the shutdown started.

“Chicago’s airports continue to provide safe and efficient operations for passengers,” Chicago Department of Aviation spokeswoman Lauren Huffman stated in an email. “We are in continuous dialogue with all of our federal partners, including the TSA, to ensure the highest level of safety and security for O’Hare and Midway Airports during the shutdown.”

Travelers at O’Hare said hearing about the union’s concerns is worrying.

“I am already scared to fly in general, and knowing that the security might not be as tightened as it normally would because there’s less workers, really, it’s frightening,” said Melissa Abraham, of Chicago.

Lauren Rozum, of Hinsdale, said it’s frightening to get on a plane with so many airport employees not working, or over-worked, due to the shutdown.

“It’s very unsettling knowing that the security controls and the officers are not working, and there’s a lot of safety inspections that are not happening,” she said.

Chris Crotty, of Gurnee, however, said he’s still confident in the safety at airports.

“I’m only going for a short stint. So hopefully they’ll have everything corrected by the weekend,” he said.

U.S. Sen. Tammy Duckworth released a statement Thursday stating, in part, “This ridiculous and unnecessary shutdown is causing serious financial hardship for hundreds of thousands of families across the country and it’s halting critical government services, putting our safety at risk.”

The senator called for an immediate end to the shutdown.