More than 1,500 flights were cancelled over the weekend and thousands more were delayed in another tough weekend for domestic travel in the United States.

Carriers have canceled 850 and delayed 4,041 flights into, within or out of the United States on Sunday, according to FlightAware. Airlines canceled 657 and delayed 7,267 U.S. flights on Saturday.

Those weekend figures add to the more than 1,400 flights canceled on Friday.

It has been a chaotic summer travel season for the airline industry, which is grappling with issues like staffing shortages, severe summer storms and high fuel costs as travel demand resurges. 

Some airlines had cut back on their August schedules in recent months to improve reliability, which has become an increasing focus in Washington.

Lawmakers and Transportation Secretary Pete Buttigieg have discussed a range of proposals, from refund regulations to fines against airlines that cancel flights.

Chicago’s Midway airport had seen the most cancellations by percentage out of any U.S. airport on Sunday, with about 14 percent of flights canceled, according to FlightAware.

Other U.S. airports with large proportions of cancellations included major carriers’ hubs, like Chicago’s O’Hare airport, Newark’s Liberty airport and LaGuardia in New York.

More than a third of flights at O’Hare — 35 percent of departing flights and 38 percent of arriving flights — had been delayed on Sunday, the most of any U.S. airport in both categories, according to FlightAware.

The National Weather Service forecasted rain and thunderstorms on Sunday morning for the Chicago area, and O’Hare reported arrival delays of roughly 45 minutes and departure delays of roughly 35 minutes as of Sunday afternoon.

Wisconsin Air, a regional carrier for United Airlines, canceled the most flights by percentage out of any U.S. carrier on Sunday so far. The carrier canceled 56 flights on Sunday, or 26 percent of its schedule, and all of those flights listed O’Hare as either the departure or arrival airport, according to Flight Aware. 

Regional carriers have seen some of the most drastic pilot shortages, with many offering pay incentives to attract and retain pilots.

The Hill has reached out to the Chicago Department of Aviation, which oversees the O’Hare and Midway airports, and Wisconsin Air for comment.

The high number of cancellations and delays come amid increased scrutiny of the industry.

Buttigieg’s department on Wednesday proposed a new rule that would strengthen existing refund regulations to require airlines to refund passengers who do not travel if the departure or arrival times change by at least three hours for a domestic flight and at least six hours for an international flight. 

The announcement came days after a group of Democratic lawmakers introduced a bill that would codify DOT’s existing regulation mandating cash refunds. 

Other Democrats, like Sen. Bernie Sanders (I-Vt.) and Pennsylvania Democratic Senate nominee John Fetterman, have separately called for imposing fines on airlines for certain schedule changes.

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