Southwest Airlines canceled hundreds more flights Monday following thousands of flight cancellations over the weekend but said it expects to resume normal service this week.
For the third straight day, passengers were left stranded amid confusion about what caused the cancellations.
Southwest blamed the weekend cancellations on bad weather and air traffic control issues in Florida. The Federal Aviation Administration acknowledged some control issues on Friday; however, it noted that no other airlines suffered large-scale cancellations throughout the weekend.
The union for Southwest's pilots has denied holding a sickout in response to the airline's decision to mandate vaccinations.
The union asked a federal court on Friday to block the airline's requirement that all employees get vaccinated against COVID-19. It says it does not oppose vaccinations but has argued that Southwest must negotiate with the union over any vaccine mandates before implementing them.
Southwest said that the initial wave of flight cancellations left aircraft and crew out of place, which in turn made it difficult for the airline to recover its normal schedules and led to more canceled flights.
In a video message to employees seen by CNBC, Southwest Chief Operating Officer Mike Van de Ven said that staffing shortages have also played a role in the service disruption.
The airline "is still not where we need to be on staffing and, in particular, with flight crews," he said.
Southwest is one of several airlines that have been struggling with staffing issues for months, leading to flight cancellations and delays throughout the summer.
Southwest said in a tweet Monday, "While we work to stabilize our operations, we anticipate to resume normal service this week."
Some information for this report came from The Associated Press, Reuters and Agence France-Presse.