The Fort Worth-based airline canceled more than 810 flights as of Sunday afternoon, accounting for 29% of its schedule, according to tracking service FlightAware. Nearly 260 of AA's Sunday flights were delayed.
On Saturday, American's flight cancelation total reached 543, with 433 delayed flights.
For comparison, the U.S.-based airline with the second-highest volume of cancelations Sunday was Southwest, with approximately 185 canceled flights.
Videos from Dallas, Miami and Charlotte, North Carolina show long lines stretching through airport terminals as customers scrambled to get to their destinations.
One Twitter user compared American's customer service lines to the wait for music festival entry.
"Flights are cancelled? Seniors, pregnant women, women traveling alone with their children waiting 4-8 hour líne, unbelievable," another Twitter user wrote.
The airline said travel troubles stemmed from two days of severe winds at Dallas/Fort Worth International Airport, its largest hub, according to an internal letter obtained by ABC News.
"This weather drove a large number of cancellations at DFW, as we could only use two runways instead of the usual five that handle our operation," the letter read.
DFW had a 13% cancelation rate Sunday, with Charlotte Douglas International Airport in North Carolina and Chicago O'Hare International Airport reporting 14% and 4% of flights canceled respectively, according to Flight Aware.
American also said staffing limitations aggravated the problem.
"To make sure we are taking care of our customers and providing scheduling certainty for our crews, we have adjusted our operation for the last few days this month by proactively canceling some flights," the letter read.
#trappedincharlotte @AmericanAir just canceled our flight from Charlotte to San Diego 45 minutes prior to departure without explanation. Their remedy? Go to customer service. This is the line: pic.twitter.com/fPk3mttiR0— Cocoon (@cocoonmusic) October 30, 2021
As air travel plunged in early 2020, airlines offered buyouts and early retirement packages to employees in order to cut costs. As they try to hire, or rehire, workers, service disruptions have become more frequent.
This comes as U.S. air travel has recovered to nearly 80% of the pre-pandemic level and the busy holiday season looms.
AA said it plans to increase staffing ahead of the fall and winter holidays, with nearly 1,800 returning from leave starting Nov. 1 and more coming back in December.
"Additionally, hiring for our airports is well underway and we anticipate 4,000 new team members joining us across the system in the fourth quarter," the company said in the internal letter.
MORE: Southwest canceled more than 2,000 weekend flights and the disruption continues
The widespread disruption harkens back to Southwest's troubles in early October, when the airline canceled nearly 2,400 flights over a three-day period. Southwest's crisis peaked Sunday, Oct. 10, with 30% of its schedule canceled.
The company blamed bad weather and air traffic control issues in Florida, but neither Southwest nor its pilots' union has provided evidence to back up their explanations, the Associated Press reported.
CNNWire contributed to this report.