These are the 40 airports where flights are being canceled due to the government shutdown

• Federal officials will cut 10% of flights at 40 US airports starting Friday.
• The reduction is due to air traffic control delays from the ongoing government shutdown.
• Up to 1,800 flights, affecting 268,000 seats, could be impacted, says Cirium.

Holiday travel is starting to look incredibly dicey.

The shutdown so far has created massive air traffic control delays, leaving some airports so understaffed that they had to temporarily shut down. Starting on Friday, federal officials will reduce the number of flights at 40 US airports to manage traffic.

This will start with a 4% reduction, ultimately ramping up to 10% by November 14.

Cirium, an aviation analytics firm, estimated that up to 1,800 flights representing about 268,000 seats could be cut on Friday.

“We are seeing signs of stress in the system, so we are proactively reducing the number of flights to make sure the American people continue to fly safely,” Bryan Bedford, the Federal Aviation Administrator, said late Thursday.

The FAA also said that all airlines will be required to issue full refunds.

Here’s its full list of the 40 airports that are affected, spanning half of all US states:

• Ted Stevens Anchorage International Airport, Alaska
• Hartsfield-Jackson Atlanta International Airport, Georgia
• Boston Logan International Airport, Massachusetts
• Baltimore/Washington International Airport, Maryland
• Charlotte Douglas International Airport, North Carolina
• Cincinnati/Northern Kentucky International Airport, Ohio and Kentucky
• Dallas Love Field, Texas
• Ronald Reagan Washington National Airport, Virginia
• Denver International Airport, Colorado
• Dallas/Fort Worth International Airport, Texas
• Detroit Metropolitan Wayne County Airport, Michigan
• Newark Liberty International Airport, New Jersey
• Fort Lauderdale/Hollywood International Airport, Florida
• Honolulu International Airport, Hawaii
• William P. Hobby Airport, Texas
• Washington Dulles International Airport, Virginia
• George Bush Houston Intercontinental Airport, Texas
• Indianapolis International Airport, Indiana
• New York John F. Kennedy International Airport, New York
• Las Vegas Harry Reid International Airport, Nevada
• Los Angeles International Airport, California
• New York LaGuardia Airport, New York
• Orlando International Airport, Florida
• Chicago Midway International Airport, Illinois
• Memphis International Airport, Tennessee
• Miami International Airport, Florida
• Minneapolis-St. Paul International Airport, Minnesota
• Oakland International Airport, California
• Ontario International Airport, California
• Chicago O’Hare International Airport, Illinois
• Portland International Airport, Oregon
• Philadelphia International Airport, Pennsylvania
• Phoenix Sky Harbor International Airport, Arizona
• San Diego International Airport, California
• Louisville International Airport, Kentucky
• Seattle-Tacoma International Airport, Washington
• San Francisco International Airport, California
• Salt Lake City International Airport, Utah
• Teterboro Airport, New Jersey
• Tampa International Airport, Florida

Holiday travel snarls

The reductions come at an especially bad time, as the busy Thanksgiving and Christmas travel seasons approach. And there appears to be some scrambling among the government, airports, and airlines to determine what can be shaved with just a few days’ notice.

Some airlines have given customers a general idea of what to expect, but details are scarce.

Frontier Airlines told Business Insider that most of its flights are expected to “operate as planned” come Friday, but will proactively communicate with customers as changes occur. It did not offer exact routes. Southwest similarly said it did not yet have specific figures.

United CEO Scott Kirby provided some information in a Wednesday statement, saying none of the airline’s long-haul international or hub-to-hub flights would be affected. Instead, he said reductions will be on regional routes — which connect hubs to smaller airports — and domestic mainline flights that do not travel between hubs.

United has seven main hubs in the mainland US: Chicago, Denver, Houston, Los Angeles, Newark, San Francisco, and Washington Dulles. It also has a hub in Guam.

United is planning to reduce its flights by 4% from Friday through the weekend, before gradually increasing that to 10%, a source close to the airline told Business Insider. That’s roughly 250 to 300 daily cancellations, affecting around 25,000 customers a day, they added.

Delta told Business Insider it was canceling about 170 out of its nearly 5,000 mainline and regional flights on Friday. American told Business Insider it would cancel about 220 of its 6,000 daily flights each day between Friday and Monday.

Cirium data estimates that Chicago O’Hare, if on the list, would be the most affected airport on Friday, with 121 flights canceled across all airlines. Atlanta — where Delta has its major hub — would be second at 104 flights.

Customers should prepare for disruptions

The schedule adjustments have created uncertainty for travelers, and some industry experts advise that travelers should prepare for longer lines and potential delays.

“If you’re checking bags, plan for long lines with extra time at the airport, and pack any valuables or time-sensitive items in your carry-on,” Audrey Kohout, Co-CEO of luggage shipping companies LuggageForward and LugLess, said in a media statement.

For those whose flights get canceled, in most cases, airlines would try to rebook them on an alternative flight.

American, Delta, Frontier, and United have said that customers will be able to change or refund their flights at no extra cost.

Southwest said that passengers whose flights are canceled will be eligible for a refund. As of noon ET, Alaska does not have a flexible travel policy in place.

Some airline CEOs are already warning people to prepare for the worst: “If your flight is canceled, your chances of being stranded are high, so I would simply have a backup ticket on another airline,” Frontier Airlines CEO Barry Biffle said in a LinkedIn post.