WASHINGTON (ABC News) — The Department of Transportation might be forced to shut down the airspace in certain parts of the country if the government shutdown continues into next week, Transportation Secretary Sean Duffy said on Tuesday.

"So if, if you bring us to a week from today, Democrats, you will see mass chaos," he said. "You will see mass flight delays. You'll see mass cancellations, and you may see us close certain parts of the airspace, because we just cannot manage it because we don't have the air traffic controllers."

Nearly 50% of all major air traffic control facilities face staffing shortages, according to the Federal Aviation Administration. Air traffic controllers are required to work without pay for the duration of the shutdown.

About 13,000 air traffic controllers are currently working without pay, according to the FAA. On Friday, the agency said that 80% of New York area staff had called out.

"These hard-working Americans have bills to pay, and they are being forced to make decisions and choices," Duffy said Monday of air traffic controllers at an unrelated event in Philadelphia. "Do they go to work as an air traffic controller, or do they have to find a different job to get resources, money, to put food on their table, to put gas in their car? And as every day goes by, I think the problem is only going to get worse, not better."

Duffy said last month that air traffic controllers could be let go if they didn't show up for work.

"When you come to work, you get paid," Duffy said Oct. 9 in remarks on Fox Business’ "Varney & Co." "If you don't come to work, you don't get paid. ... If we have some on our staff that aren't dedicated, we're going to let them go."

But the transportation secretary softened that stance over the weekend, telling CBS' "Face the Nation" that he would not fire any air traffic controllers for not showing up to work.

"They need support, they need money, they need a paycheck. They don't need to be fired," he said.

Duffy made similar comments about closing airspace during an interview with ABC News' "This Week" co-anchor Martha Raddatz on Sunday.

"We will delay, we will cancel, any kind of flight across the national airspace to make sure people are safe" amid the shortages, Duffy said, while at the same time a ground stop was in effect at Newark Liberty International Airport due to staffing issues.

"There is a level of risk that gets injected into the system when we have a controller that's doing two jobs instead of one," he added.