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Hours after the Federal Aviation Administration said it planned to cut 10% of flights across 40 major airports Friday as the U.S. government shutdown drags on, Chicago-based United Airlines released a statement to about which flights and routes would be impacted. The messaged, titled "An Update on the Government Shutdown from Scott Kirby to United Employees," confirmed the reductions are set to start Nov. 7, with the airline set to make "rolling updates" to its schedule in an effort to give customers advance notice. "We'll use our app, website and push notifications to communicate to customers directly if their flight changes, and to offer rebooking options," Untied said. "We want to provide them with as much information as we can and in a way that's simple and easy to understand." According to the FAA, thousands of flights at "high-traffic" airports across the country will be cut or canceled starting Friday. The decision, the FAA and U.S. Transportation Secretary Sean Duffy said, was based on where air traffic controllers are feeling the most pressure. The FAA, which directs more than 44,000 flights a day, including commercial passenger flights, cargo planes and private aircraft, said restrictions will remain in place as long as necessary. A list obtained by NBC News showed Chicago's O'Hare and Midway International Airports will be among those impacted. FAA administrator Bryan Bedford said the FAA was set to "implement measures with our commercial airline industry partners," but that the impacts would be felt beyond commercial airspace. According to United, the airline's long-haul international flying and hub-to-hub flying will not be impacted by the schedule reduction. Local "Instead, we will focus our schedule reductions on regional flying and domestic mainline flights that do not travel between our hubs," Kirby said. According to the airline, United has seven hubs in the U.S. as part of its "hub and spoke model" – Chicago O'Hare, Denver, Houston Intercontinental, Los Angeles, Newark Liberty, San Francisco and Washington Dulles. Kirby added that customers traveling during this period are eligible for a refund, even if their flights aren't impacted. A spokesperson for Southwest Airlines, which operates up to 250 daily departures from Midway, told NBC Chicago the airline is "evaluating how the planned FAA flight reductions will affect our schedule and will communicate directly with customers as soon as possible." "Nothing is more important to Southwest than the Safety of our Customers and Employees," the spokesperson said. "We continue to urge Congress to immediately resolve its impasse and restore the National Airspace System to its full capacity." In a statement sent to NBC Chicago, the Chicago Department of Aviation said it is "monitoring the situation closely" as it awaits further details on potential impacts at Midway and O'Hare. "Our team will continue coordinating with airline and federal partners to help minimize any disruptions," the statement said. What airports will see flight cuts? NBC News obtained the following list of impacted airports Wednesday, with the FAA expected to put out an official release Thursday. ANC – Anchorage International ATL – Hartsfield–Jackson Atlanta International BOS – Boston Logan International BWI – Baltimore/Washington International CLT – Charlotte Douglas International CVG – Cincinnati/Northern Kentucky International DAL – Dallas Love Field DCA – Ronald Reagan Washington National DEN – Denver International DFW – Dallas/Fort Worth International DTW – Detroit Metropolitan Wayne County EWR – Newark Liberty International FLL – Fort Lauderdale–Hollywood International HNL – Honolulu International HOU – William P. Hobby (Houston Hobby) IAD – Washington Dulles International IAH – George Bush Intercontinental (Houston) IND – Indianapolis International JFK – John F. Kennedy International (New York) LAS – Harry Reid International (Las Vegas) LAX – Los Angeles International LGA – LaGuardia (New York) MCO – Orlando International MDW – Chicago Midway International MEM – Memphis International MIA – Miami International MSP – Minneapolis–St. Paul International OAK – Oakland International ONT – Ontario International ORD – Chicago O’Hare International PDX – Portland International PHL – Philadelphia International PHX – Phoenix Sky Harbor International SAN – San Diego International SDF – Louisville International SEA – Seattle–Tacoma International SFO – San Francisco International SLC – Salt Lake City International TEB – Teterboro TPA – Tampa International Why are flights being cut? The measure come days after Duffy warned of "mass chaos, cancelations and flight delays" if lawmakers allow the government shutdown to continue. The cuts amount to a 10% reduction in flights at 40 airports across the country, Duffy said Wednesday during a press conference with Federal Aviation Administrator Bryan Bedford. "We are seeing pressures build in a way that we don't feel if we allow it to go unchecked, will allow us to continue to tell the public that we operate the safest airline system in the world, and we're not going to react to that, and we intend to be proactive," Bedford said. 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. “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,” Bedford added. “We’re in new territory in terms of government shutdowns.” Overall, 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.