A commercial airliner takes off past the air traffic control tower at San Diego International Airport during the first day of a partial U.S. government shutdown in San Diego, California, U.S., October 1, 2025. REUTERS/Mike Blake

By Doyinsola Oladipo and David Shepardson

NEWARK/WASHINGTON (Reuters) -The number of air traffic controllers calling in sick since the government shutdown began has seen a slight "tick up", U.S. Transportation Secretary Sean Duffy said on Monday, at times cutting air traffic staffing by 50% in some areas.

Duffy did not specify where the staffing issues were occurring, but 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 Oct. 14.

Delays will result from the reduced staffing, Duffy said, adding that if sick calls increase, air traffic flow will be cut to a rate that maintains air safety.

In some airports, there was a 50% reduction in air traffic staffing on certain days, he added. Denver, Fort Worth, Texas, and Phoenix on Monday saw a rise in sick calls from air traffic controllers, according to the USDOT.

President Donald Trump has made transportation a focal point in a government shutdown battle with the Democrats, cutting off more than $28 billion of aid for climate programs, subways, tunnels and mass transit in Democratic-leaning states like New York and Illinois.

Duffy and the president of the National Air Traffic Controllers Association spoke at a press conference at Newark Liberty International Airport to discuss the effects of the shutdown. The airport is one of three serving the heavily Democratic-leaning New York metropolitan area and is a major United Airlines hub.

In 2019, during a 35-day shutdown, the number of absences by controllers and Transportation Security Administration officers rose as workers missed paychecks, extending checkpoint wait times at some airports. Authorities were forced to slow air traffic in New York, which put pressure on lawmakers to quickly end the standoff.

Duffy noted controllers are worried. "They're thinking about, am I going to get a paycheck?," Duffy said, adding that some are asking themselves: "Do I have to take a second job and drive Uber when I'm already exhausted from doing a job that's already stressful?"

The union on Monday reminded workers, "participating in a job action could result in removal from federal service" and that it is illegal.

"It is more important than ever that we rise to the occasion and continue delivering the consistent, high-level of public service we provide every day," the union told members. "We cannot stress enough that it is essential to avoid any actions that could reflect poorly on you, our union, or our professions."

NATCA in 2019 said many controllers had reached "the breaking point." Then-House Speaker Nancy Pelosi, a Democrat, said at the time the shutdown was "pushing our airspace to the breaking point."

Airline trade group Airlines for America, which represents United, Delta Air Lines, American Airlines and Southwest Airlines, warned that during a funding lapse "the system may need to slow down, reducing efficiency" and impacting travelers.

A persistent shortage of controllers has delayed flights and many are working mandatory overtime and six-day weeks. The FAA is about 3,500 air traffic controllers short of targeted staffing levels.

(Reporting by David Shepardson; Editing by Bill Berkrot, Nick Zieminski and Chris Reese)