There have already been numerous delays at airports across the country — sometimes hours long — because the Federal Aviation Administration slows down or stops traffic temporarily anytime it is short on controllers. Last weekend saw some of the worst staff shortages and on Sunday, flights at Newark Liberty International Airport in New Jersey were delayed for several hours.

Duffy and the head of the air traffic controllers union have both warned that the situation will only get worse the longer the shutdown continues and the financial pressure continues to grow on people who are forced to work without pay. FAA employees already missed one paycheck on Oct. 28. Their next payday is scheduled for next Tuesday.

“Many of the controllers said ‘A lot of us can navigate missing one paycheck. Not everybody, but a lot of us can. None of us can manage missing two paychecks,’” Duffy said. “So if you bring us to a week from today, Democrats, you will see mass chaos. 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 air traffic controllers.”

Most of the flight disruptions so far during the shutdown have been isolated and temporary. But if delays become more widespread and start to ripple throughout the system, the pressure will mount on Congress to reach an agreement to end the shutdown.

Major airlines, aviation unions and the travel industry have been urging Congress to end this shutdown as soon as possible by voting to support the clean funding resolution that Republicans have proposed.

The U.S. Travel Association said in a letter to Congressional leaders this week that the economy has already lost more than $4 billion because of the shutdown, and the industry worries the impact will get significantly worse if the shutdown continues into the holiday travel season.

“With Thanksgiving, the busiest travel period of the year, imminently approaching, the consequences of a continued shutdown will be immediate, deeply felt by millions of American travelers, and economically devastating to communities in every state,” the U.S. Travel Association said.

Normally, airlines strive to have at least 80% of their flights depart and arrive within 15 minutes of when they are scheduled. Aviation analytics firm Cirium said that since the shutdown began on Oct. 1, the total number of delays overall has not fallen significantly below that goal because most of the disruptions so far have been no worse than what happens when a major thunderstorm moves across an airport.

But on Sunday, only about 56% of Newark’s departures were on time, and the Orlando airport reported that only about 70% of its flights were on time, according to Cirium.

As of midday Tuesday, there have been 1,932 flight delays reported across the United States, according to www.FlightAware.com. That is lower than what is typical although the FAA did say that flights in Phoenix were being delayed Tuesday morning because of staffing shortages. Strong winds are also causing delays at the Newark and LaGuardia airports Tuesday.