As the U.S. federal government shutdown entered its 40th day on Sunday, more than 2,000 flights were canceled and over 8,000 delayed nationwide, according to flight tracking website FlightAware.

Since the Federal Aviation Administration's (FAA) mandated flight reduction policy took effect on Friday, the number of canceled flights surged from 202 on Thursday to 1,025 on Friday, and further to 1,566 on Saturday.

The number of air traffic controllers taking leave has risen since the shutdown began on Oct. 1, forcing many others to work overtime.

The U.S. Department of Transportation and the FAA recently announced a 10 percent capacity reduction at 40 major airports across the country starting Friday, aiming to ease staffing pressures and reduce airspace safety risks.

"It's only going to get worse," Transportation Secretary Sean Duffy told CNN on Sunday. "I look to the two weeks before Thanksgiving. You're going to see air travel be reduced to a trickle."

On the same day, National Economic Council Director Kevin Hassett told CBS that if people are not traveling during Thanksgiving, "we really could be looking at a negative quarter for the fourth quarter."