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"Large-scale cancellations are expected today," Delta said in an earlier statement from 7:30 a.m. ET.
Fliers took to social media with images of growing lines at a number of locations served by Delta.
“The timing of this problem is particularly bad because Monday morning is one of the busiest times for both airlines and travelers as business travelers begin their work week,” Daniel Baker, CEO of flight-tracking service FlightAware, said Monday.
In response to the disruptions, Delta is waiving change fees for customers ticketed to travel this week. The airline says customers booked on a flight from Monday through Friday can make one change to their itinerary without paying the standard fee, which ranges from $200 domestically to as much as $500 on some international itineraries. Delta says rebooked travel must be for flights no later than Friday.