Air travelers are experiencing the effects of the longest U.S. government shutdown, as they are compelled to contend with disruptions due to an inadequate number of active air traffic controllers.

Moreover, air travel is poised to become considerably more inconvenient, following Transportation Secretary Sean Duffy’s announcement on Wednesday that he is mandating a 10% reduction in flights at 40 major U.S. airports, citing concerns over air traffic control safety.

The Federal Aviation Administration (FAA) is scheduled to release an order on Thursday, formalizing this decision, with the cuts anticipated to become effective on Friday. The FAA has also cautioned that it might impose further flight restrictions in the future, should additional air traffic issues emerge.

“In my 35-year tenure in the aviation market, I am unaware of a situation where we’ve had to implement measures of this nature. We are in unprecedented territory concerning government shutdowns,” stated FAA Administrator Bryan Bedford during a press conference on Wednesday.

The FAA is approximately 3,500 air traffic controllers short of its typical staffing levels, and many have been working demanding schedules filled with overtime shifts and six-day weeks.

Duffy had previously raised concerns about air travel safety in early October.

“I want them [air traffic controllers] to concentrate on the departures and arrivals of aircraft. I want to ensure they keep Americans, and airplanes, safe,” Duffy remarked during a press conference at Newark Liberty International Airport in New Jersey. “But their thoughts aren’t solely on the airspace; they’re contemplating: ‘Will I receive a paycheck?’ ‘How will I pay my mortgage?’ ‘How do I make my car payment?’ ‘Do I have to take a second job and drive Uber?’”

On Oct. 30, an urgent appeal was issued for the government shutdown to conclude, characterized as an “unsustainable crisis.”

“Air traffic controllers, TSA officers, and other personnel required to work without pay missed their first full paycheck this week,” they commented, additionally highlighting worries that “over 40 million people, including flight attendants, will [soon] lose [benefits/income].”

Airlines are now preparing for the flight reductions and formulating plans to support their customers during this period.

“Any passenger traveling during this time is eligible for a refund if they choose not to fly—even if their flight is not affected. This includes non-refundable tickets and those customers with basic economy tickets,” United Airlines CEO Scott Kirby informed TIME in an emailed statement on Thursday morning.

According to Kirby, United will provide “rolling updates” regarding the forthcoming changes, aiming to give “customers several days’ advance notice and to minimize disruption for them.”

The airline’s international long-haul flights and “hub-to-hub flying” are not expected to be impacted by the FAA directive. Its hub airports include Chicago O’Hare, Denver International, Guam’s Antonio B. Won Pat, Houston George Bush, Los Angeles International, Newark Liberty, San Francisco International, and Washington Dulles.

Delta Airlines conveyed to TIME that it “anticipates operating the vast majority of [its] flights as scheduled, encompassing all long-haul international services.” The company emphasized that safety is the “foremost priority.”

As concerns regarding air travel safety escalate, and the inconvenience for passengers is set to increase, here is what you need to know:

What is causing the numerous flight delays and cancellations?

On Wednesday alone, U.S. airports recorded almost [a significant number of delays] and over 170 cancellations.

Due to some staff not reporting for duty without pay, Duffy stated that those who are working face immense pressures.

“They are working longer hours, they are working more days, and that’s some of the pressure we are observing on them, and we aim to alleviate that pressure before it becomes a problem,” he said, outlining his strategy for cuts.

Citing performance data, the FAA echoed Duffy’s concerns, with Bedford telling the press: “We are beginning to see some evidence that fatigue is accumulating in the system… we need to work towards relieving some of that strain.”

Which airports will experience the flight reductions?

Neither Duffy nor Bedford confirmed on Wednesday which specific airports would see a reduction in their traffic, but stated that it would not be based on particular airlines. Further information is expected shortly.

“We have identified 40 high-traffic market environments. We will be pleased to share that later,” Bedford announced.

[According to available data], the 40 busiest airports in the U.S. in 2024 each saw over 5 million passengers pass through.

These airports included Hartsfield-Jackson International in Atlanta with 52.5 million passengers, Dallas-Fort Worth International with 42.3 million, and Denver International with 40 million. Chicago O’Hare, Los Angeles International, and JFK International in New York all served over 25 million passengers in 2024.

So far this week, Hartsfield-Jackson International has experienced 762 delays and 20 cancellations, with Dallas-Fort Worth encountering 825 delays and six cancellations, and Denver International has managed 594 delays and 12 cancellations, according to Flight Aware.

“We have determined that a 10% reduction in scheduled capacity would be appropriate to, once again, continue to alleviate pressure on our controllers, and as we continue to observe staffing triggers, additional measures will be implemented in those specific markets,” said Bedford. “We are aiming for a significant reduction across these 40 markets within the next 48 hours.”

When questioned about the duration of these reductions, Duffy stated that it would depend on the data that the FAA and Department for Transport are currently examining.