Southwest Airlines (WN, Dallas Love Field) continues to suffer the fallout from a wave of flight cancellations over October 8-10, 2021, but has vehemently denied the original cause was a staff shortage triggered by plans to enforce a federal COVID vaccination mandate among its crews.

The low-cost carrier has cancelled around 2,400 flights since October 8. Over the weekend, it cancelled around a third of all of its scheduled flights. While since then, the number of disruptions has decreased, the New York Times reported that some 10% of all flights were cancelled on Monday. On Tuesday, the rate stood at 2%.

"I know it's been a really rough weekend, and obviously, I really feel for our customers and our people that are trying their best to serve our customers, but when an airline gets behind, it's hard to catch up," Chief Executive Gary Kelly told CNBC.

Southwest claimed the initial cause was inclement weather, military training, and a staff shortage at an air traffic control centre, which disrupted the carrier's crew scheduling efforts. As a result, 71% of its pilots had to be reassigned to other flights on Saturday and 85% on Sunday, compared to the average rate of around 10%. Due to the scale of the disruption and Southwest's point-to-point network, many crew members could not get to their flights on time.

Some early reports had attributed the chaos to industrial action on the part of pilots against the planned vaccination mandate. However, the Southwest Airlines Pilots Association has since stressed that there was no unusual rate of sick leaves among its members and attributed the disruptions to Southwest's poor planning. The union is challenging the mandatory vaccination requirement - while it does not oppose the inoculations as such, it alleges the carrier's decision is in breach of labour law.

President Joe Biden mandated all federal government contractors to have all of their staff vaccinated (except for those with medical exemptions) by December 8, 2021. Southwest Airlines and American Airlines, which are both incorporated in Texas, reiterated they would comply with the executive order despite the decision by Governor Greg Abbott banning any large employer in the state from requiring vaccinations.

"Federal action supersedes any state mandate or law, and we would be expected to comply with the President's Order to remain compliant as a federal contractor," Southwest Airlines told Politico.