The U.S. Federal Aviation Administration said staffing issues were causing delays at several airports on Monday, just hours after the top U.S. transportation official said air traffic controllers calling in sick had risen slightly since the government shutdown began.
Some 13,000 air traffic controllers and about 50,000 Transportation Security Administration officers must still turn up for work during the shutdown. They are not being paid and controllers are set to miss their first paycheck on October 14.
Transportation Secretary Sean Duffy said that, at times, air traffic staffing has been cut by 50% in some areas since the shutdown started last week.
FlightAware said more than 4,000 flights in the U.S. on Monday were delayed, including 29% arriving flights at Denver, 19% of Newark flights and 15% of Las Vegas flights. Weather issues are also impacting flights.
Read More: American Journal of Transportation