[Source: Reuters]

Airlines canceled more than 2,200 U.S. flights on Sunday.

Transportation Secretary Sean Duffy warned air travel will fall to a “trickle” in the run-up to the Thanksgiving holiday as air traffic control staffing shortages surge during the federal shutdown.

Major airlines were dealing with a third day of government-mandated flight cuts after thousands of delays and cancellations snarled traffic on Saturday.

The shutdown, which has reached a record 40 days, has led to shortages of air traffic controllers who, like other federal employees, have not been paid for weeks.

“It’s only going to get worse… the two weeks before Thanksgiving, you’re going to see air travel be reduced to a trickle,” Duffy said on CNN’s “State of the Union” program.

Millions of people usually travel in the run-up to Thanksgiving, one of the most important U.S. holidays, which this year falls on November 27.

“Many of them are not going to be able to get on an airplane, because there are not going to be that many flights that fly if this thing doesn’t open back up,” Duffy said.

Sunday’s cancellations were the single worst day for flight cancellations since the shutdown began on October 1.

The Federal Aviation Administration instructed airlines to cut 4% of daily flights starting on Friday at 40 major airports because of air traffic control safety concerns. Reductions in flights are mandated to reach 6% on Tuesday and then hit 10% by November 14.

Many airlines have already planned their cancellations for the coming days. United Airlines, for example, will cut 190 flights on Monday and 269 on Tuesday, the company said.

As of 4:20 p.m. ET (2120 GMT) on Sunday, data from flight tracking site FlightAware indicated there had already been 2,215 U.S. flight cancellations and more than 7,200 delays as conditions looked to be worsening.

The Federal Aviation Administration earlier in the day said it had staffing issues at 12 towers.

A growing number of air traffic controllers have retired since the federal shutdown started on October 1, Duffy said. The FAA is 1,000 to 2,000 controllers short of full staffing, he told CNN.

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