Transportation Secretary Sean Duffy said controllers were “wearing thin” as they continued to work without pay. Some flights on the Californian coast were grounded over the weekend due to staffing shortages.

He told Fox News: “The controllers are wearing thin.

“I am seeing the stress.

“They're taking second jobs, they're out there looking, 'Can I drive Uber, can I find another source of income to make ends meet?'"

The shutdown, which began on 1 October, has left thousands of federal employees unpaid. Air traffic controllers, considered essential workers, have been required to stay on duty but are now struggling to manage workloads and personal finances.

On Saturday, the Department of Transportation issued 22 alerts warning that flights would be delayed due to low staffing — one of the highest numbers since the shutdown began. The Federal Aviation Administration (FAA) confirmed that more than 3,000 US flights were delayed on Sunday, with airports from Los Angeles to Newark affected.

Some planes were grounded at Los Angeles International Airport early Sunday morning, with operations returning to normal before noon. Newark Liberty International Airport saw average delays of 82 minutes, and the FAA said Dallas Fort-Worth could also face disruption later in the day.

Duffy said the government might have to slow the number of flights if staffing levels continued to fall. When asked if it was still safe to fly, he avoided a direct answer, instead making a plea to controllers.

He said: “I need my controllers focused on the airspace, not on the finances at home."

The crisis comes just weeks before the Thanksgiving travel period, one of the busiest times for US air travel. Strain on the aviation system helped end the 2019 government shutdown, when mass absences by controllers briefly halted flights at New York’s LaGuardia Airport.