Duffy said the government shutdown is most likely taking a toll on already overburdened controllers.

"Now what they think about as they’re controlling our airspace is: ‘How am I going to pay my mortgage? How do I make my car payment? I have a couple kids at home, how do I put food on the table?'" Duffy said. "'I’m working six days a week, so I have to take a second job and drive Uber when I’m already exhausted from doing a job that’s already stressful, to think about how I can make extra money because the government may not provide me a paycheck?'"

NATCA President Nick Daniels also called for an end to the shutdown.

"We do not have the luxury of time," he said at a news conference in Newark. "We do not have time to waste on the unnecessary distractions created by this shutdown."

"Our message is clear: End the shutdown," he added.

On Tuesday evening, Nashville International Airport was experiencing delays that averaged around two hours because of staffing issues, the FAA said on its website.

The Metropolitan Nashville Airport Authority said the FAA notified it at 1:25 p.m. that arriving and departing traffic at the airport would be reduced because of a shortage of air traffic controllers.

At O'Hare International Airport in Chicago, the FAA said, delays averaged 41 minutes Tuesday because of staffing.

Flights at Dallas-Fort Worth International Airport faced delays of around 30 minutes late Tuesday afternoon, but the delay times were decreasing, the FAA said.

On Monday, staffing issues left Hollywood Burbank Airport in the Los Angeles area with no air traffic controllers. Another agency handled the workload. The airport, which is a smaller one, said Monday evening on X that it was still operational.

Eric Everts, a spokesperson for Phoenix Sky Harbor International Airport, said in a statement that the airport "does not anticipate many visible impacts to operations in the short term due to the federal government shutdown, as most essential workers are required to continue working without pay."

Everts encouraged passengers to confirm their flight statuses and arrive early before their flights, especially "during this busy fall break period."

The Senate again failed to pass legislation Monday night that would reopen the government, and there are no signs of a deal between Democrats and Republicans in the immediate future.

Matt Lavietes is a reporter for NBC News.

Corky Siemaszko is a senior reporter for NBC News Digital.

Phil Helsel and Jay Blackman contributed.