WASHINGTON (AP) — U.S. airlines began canceling hundreds of flights Thursday due to the Federal Aviation Administration’s order to reduce traffic at the country’s busiest airports starting Friday because of the government shutdown.

More than 790 planned Friday flights were cut from airline schedules, according to FlightAware, a website that tracks flight disruptions. That number, already four times higher than Thursday’s daily total, was likely to keep climbing.

The 40 airports selected by the FAA span more than two dozen states and include hubs such as Atlanta, Dallas, Denver, Los Angeles and Charlotte, North Carolina, according to the agency’s order, which was published Thursday evening. In some metropolitan areas, including New York, Houston, Chicago and Washington, multiple airports will be impacted.

The FAA said in the order that the reductions will start Friday at 4% and ramp up to 10% by Nov. 14. They are to be in effect between 6 a.m. to 10 p.m. local time and impact all commercial airlines.

The decision to reduce service at “high-volume” markets is meant to maintain travel safety as air traffic controllers exhibit signs of strain during the shutdown. It also comes as the Trump administration is ramping up pressure on Democrats in Congress to end the shutdown.

“With continued delays and unpredictable staffing shortages, which are driving fatigue, risk is further increasing, and the FAA is concerned with the system’s ability to maintain the current volume of operations,” the order reads.

Hours before the reductions went into place, airlines were scrambling to figure out where to cut. American Airlines said it reduced its schedule at the listed airports by 4% from Friday through Monday, about 220 cancellations each day, and would move from there toward the 10% target. The carrier said its international schedule was expected to remain untouched.

Passengers with plans for the weekend and beyond waited nervously to see if their flights would take off as scheduled. Some travelers began changing or canceling itineraries preemptively.

Flight cuts may impact smaller carriers

The restrictions also apply to a subset of smaller carriers that operate scheduled charter flights. International flights do not have to be reduced, according to the FAA.

Some airlines planned to focus on slashing routes to and from small and medium-size cities.

“This is going to have a noticeable impact across the U.S. air transportation system,” industry analyst Henry Harteveldt said.

The flight reductions just weeks before the busy holiday season prompted some travelers to change their plans or look at other options.

Fallon Carter canceled her Friday flight from New York to Tampa, Florida, where she planned to spend the weekend at the beach. She was worried about making it back to Long Island to be a bridesmaid at her best friend’s wedding.

“I don’t know if I get there, will I get home?” Carter said.

The FAA is imposing the reductions to relieve pressure on air traffic controllers who are working without pay during the shutdown, which began Oct. 1, and have been increasingly taking sick days. Most controllers work mandatory overtime six days a week, leaving little time for side jobs to help cover bills unless they call out.

In recent weeks the FAA has delayed flights when airports or its other facilities are short on controllers.

Shuffling schedules

Airlines said they would try to minimize impact on customers, some of whom will see weekend travel plans disrupted with little notice.

The airlines will be required to issue full refunds but not to cover secondary costs such as food and hotel accommodations unless a delay or cancellation results from a contributing factor that is within the control of the airlines, according to the Department of Transportation.

The head of Frontier Airlines recommended that travelers buy backup tickets with another airline to avoid being stranded.

The cuts also could disrupt package deliveries because two airports with major distribution centers are on the list — FedEx operates at the airport in Memphis, Tennessee, and UPS in Louisville, Kentucky, the site of this week’s deadly cargo plane crash.

The FAA also said commercial space launches will only be allowed between 10 p.m. and 6 a.m. starting Monday. That could force SpaceX to reschedule some upcoming planned afternoon launches.

The cuts could affect as many as 1,800 flights, or upward of 268,000 passengers, per day, according to an estimate from Cirium.

Airlines are used to dealing with canceling thousands of flights on short notice during severe weather, but the difference now is that these cuts during the shutdown will last indefinitely until safety data improves.

Shutdown already straining travel

The shutdown is putting unnecessary strain on the system and damaging confidence in the U.S. air travel experience, said U.S. Travel Association President and CEO Geoff Freeman.

Kelly Matthews, who lives in Flat Rock, Michigan, and flies every week, said she canceled most of her upcoming trips and understands why federal airport employees have stopped showing up.

“You can’t expect people to go in to work when they’re not getting a paycheck for the continuation of over a month now,” she said. “I mean it’s not a matter of them not wanting to do the job — but you can’t afford to pay for gas, your day care and everything else.”

Controller staffing worsening

The past weekend brought some of the worst staffing issues since the start of the shutdown.

From Friday to Sunday evening, at least 39 air traffic control facilities reported potential staffing limits, according to an AP analysis of operations plans shared through the Air Traffic Control System Command Center system. The figure, which is likely an undercount, was well above the average for weekends before the shutdown.

WASHINGTON (AP) — The Federal Aviation Administration said Wednesday that it was taking the extraordinary step of reducing air traffic by 10% across 40 “high-volume” markets beginning Friday morning to maintain travel safety as air traffic controllers exhibit signs of strain during the ongoing government shutdown.

The cutback stands to impact thousands of flights nationwide because the FAA directs more than 44,000 flights daily, including commercial passenger flights, cargo planes and private aircraft. The agency didn’t immediately identify which airports or cities will be affected but said the restrictions would remain in place as long as necessary.

“I’m not aware in my 35-year history in the aviation market where we’ve had a situation where we’re taking these kinds of measures,” FAA Administrator Bryan Bedford said at a news conference.

Air traffic controllers have been working unpaid since the shutdown began Oct. 1, and most have been on duty six days a week while putting in mandatory overtime. With some calling out of work due to frustration, taking second jobs or not having money for child care or gas, staffing shortages during some shifts have led to flight delays at a number of U.S. airports.

Bedford, citing increased staffing pressures and voluntary safety reports from pilots indicating growing fatigue among air traffic controllers, said he and U.S. Transportation Secretary Sean Duffy did not want to wait until the situation reached a crisis point.

“We’re not going to wait for a safety problem to truly manifest itself when the early indicators are telling us we can take action today to prevent things from deteriorating,” Bedford said. “The system is extremely safe today and will be extremely safe tomorrow. If the pressures continue to build even after we take these measures, we’ll come back and take additional measures.”

He and Duffy said they would meet with airline executives later Wednesday to determine how to implement the reduction in flights before a list of the affected airports would be released sometime Thursday.

Airlines and passengers wait for information

United, Southwest and American all said they will try to minimize the impact on consumers as they cut their schedules to comply with the order.

Calls to the customer service hotlines at United and American were answered within a few minutes Wednesday afternoon, suggesting anxious passengers were not swamping the airlines with questions about the status of their upcoming flights.

In a letter to employees, United CEO Scott Kirby promised to focus the cuts on regional routes and flights that don’t travel between hubs. He said the airline will try to reschedule customers when possible and will also offer refunds to anyone who doesn’t want to fly during this time, even if their flight isn’t canceled.

“United’s long-haul international flying and our hub-to-hub flying will not be impacted by this schedule reduction direction from the FAA,” Kirby said. “That’s important to maintain the integrity of our network, give impacted customers as many options as possible to resume their trip, and sustain our crew pairing systems.”

Airline industry analyst Henry Harteveldt, who is president of Atmosphere Research Group, said he thinks the government may have bungled this announcement by not meeting with airlines first and giving them more time to adjust schedules made months in advance.

“To tell airlines you’ve got 48 hours to rebuild your schedules at 90% of what you’ve got isn’t much time, and it’s going to result in a lot of chaos,” said Harteveldt, who was waiting to hear if his own flight from San Francisco to Dallas on Saturday would be canceled. He added that the Trump administration may be using aviation safety “to force the two sides in Washington back to the negotiating table to resolve the shutdown.”

AAA spokesperson Aixa Diaz advised travelers to watch for flight updates on the airline’s app and airport social media accounts. She also recommended allowing plenty of time at the airport before a scheduled flight.

“It’s frustrating for travelers, because there’s not much you can do. At the end of the day, you either fly or you don’t,” she said.

The cuts could represent as many as 1,800 flights and upward of 268,000 seats combined, according to an estimate by aviation analytics firm Cirium. For example, O’Hare International Airport in Chicago could see 121 of its 1,212 flights currently scheduled for Friday cut if the FAA distributes the reductions equally among impacted airports, Cirium said.

Data shows worsening weekend staffing

The FAA regularly slows down or stops flights from taking off toward an airport for a number of reasons, including weather conditions, equipment failures and technical problems. Staffing shortages also may lead to slowed or halted departures if there aren’t enough controllers and another facility can’t absorb some of the work load.

Last weekend saw some of the worst staffing shortages of the shutdown, which became the longest on record early Wednesday.

From Friday to Sunday evening, at least 39 different air traffic control facilities announced there was some potential for limited staffing, according to an Associated Press analysis of operations plans sent through the Air Traffic Control System Command Center system. The figure, which is likely an undercount, is well above the average for weekends before the shutdown

During weekend periods from Jan. 1 to Sept. 30, the average number of airport towers, regional centers overseeing multiple airports and facilities monitoring traffic at higher altitudes that announced the potential for staffing issues was 8.3, according to the AP analysis. But during the five weekend periods since the shutdown began on Oct. 1, the average more than tripled to 26.2 facilities.

Travel industry joins unions in urging shutdown’s end

Major airlines, aviation unions and the wider travel industry have urged Congress to end the shutdown.

Wednesday’s announcement came on the heels of Duffy warning a day earlier that there could be chaos in the skies next week if the shutdown drags on long enough for air traffic controllers to miss their second full paychecks next Tuesday.

Duffy said the FAA wanted to take a proactive approach instead of reacting after a disaster. He pointed to all the questions that arose after the deadly midair collision in January between a commercial jet and a military helicopter near Ronald Reagan Washington National Airport about why FAA didn’t recognize the risks and act sooner.

“We learned from that. And so now we look at data, and before it would become an issue, we try to assess the pressure and try to make moves before there could be adverse consequences,” Duffy said. “And that’s what’s happening here today.”