() Travelers in the United States are dealing with airline delays amid the ongoing federal government shutdown.

The government shut down on Oct. 1 after lawmakers failed to pass a bill to fund the federal government for the upcoming fiscal year. The shutdown has already contributed to airline delays nationwide and has had dire implications for the U.S. travel economy.

Since the shutdown began, many air traffic controllers have not shown up for work, massively contributing to the delays Americans are experiencing.

Air traffic controller shortage contributing to delays

Air traffic controllers are considered essential government employees, and about 13,000 are required to continue working without pay during the shutdown, according to the Department of Transportation’s contingency plan.

Between Monday and Tuesday of this week, approximately 10,000 flights were delayed. On Wednesday, an additional 3,000 flights were delayed, though weather may have contributed to some of them, as reported by affiliate The Hill.

Airports in and near major cities like New York, Chicago, Los Angeles, Nashville and the District of Columbia have experienced delays.

Airports were already dealing with staffing shortages, and the government shutdown has exacerbated the problem. As of May 7, only two of the 313 air traffic control facilities in the U.S. met staffing targets set by the Federal Aviation Administration.

Transportation Sec. Duffy responds

On Wednesday, Transportation Secretary Sean Duffy said that delays are 10 times more likely due to air traffic controller staffing shortages.

“Historically, there’s about 5% of delays attributed to staffing issues in our towers,” Duffy said Wednesday on Fox News’ “The Will Cain Show.” “The last couple of days, it’s been 53%.”

On Thursday, Duffy told Fox Business that he may fire air traffic controllers who haven’t shown up for work.

“If we have some on our staff that aren’t dedicated, we’re going to let them go,” he said.

Airline leaders and travel safety analysts warn that if the shutdown continues, the system could erode further.

“Air traffic controllers don’t start a shutdown, and we don’t end a shutdown. Politicians are the ones that start the shutdown, and they’re the only ones that have the ability to end the shutdown,” National Air Traffic Controllers Association President Nick Daniels told CNN.

One week of the shutdown has cost US travel economy $1B

According to the U.S. Travel Association, one week of the government shutdown has already cost the U.S. travel economy $1 billion. It’s estimated to continue to affect the travel economy at the same rate as the shutdown continues.

“This shutdown is doing real, irreversible damage,” said Geoff Freeman, president and CEO of the U.S. Travel Association.

affiliate The Hill contributed to this report.