Southwest Airlines canceled dozens of flights out of Nashville over the weekend, joining a trend nationwide that forced the company to cancel hundreds of flights.

After leaving hundreds of passengers stranded, the airline blamed air traffic control and weather issues for the string of cancellations.

“ATC issues and disruptive weather have resulted in a high volume of cancellations throughout the weekend while we work to recover our operation. We appreciate your patience as we accommodate affected Customers, and Customer Service wait times are longer than usual,” the company said on Twitter.

However, according to CNBC, multiple airlines who operate in similar regions did not cancel flights at the same level as Southwest.

As the delays and cancellations continued, the Southwest Airlines Pilots Association (SWAPA) slammed the airline.

“Our Pilots will continue to overcome SWA management’s poor planning, as well as any external operational challenges, and remain the most productive Pilots in the world,” the company said in a statement.

The high volume of disruptions has led several to speculate that resistance to the company’s coronavirus vaccine mandate is behind the mass cancellations.

“Major delays and cancellations for passengers flying Southwest Airlines. The airline is reporting an air traffic management program put in place because of weather is causing the flight back-ups. However, some passengers are hearing that some employees have walked off the job,” tweeted Jewell Hillery, a reporter for WGN.

“Airline sources: mass “sickout” @FAANews center in Jacksonville – caused ripple effect and 1000+ flight cancellations mostly effecting @SouthwestAir – report “sickout” protesting #VaccineMandate,” added NewsNation Now anchor Leland Vittert.

Additionally, according to a report from Alex Berenson, the Southwest Airlines Pilots Association will not acknowledge the widespread “sickout” due to a previous negotiation with the company.

“Essentially, the union cannot organize or even acknowledge the sickout, because doing so would make it an illegal job action,” Berenson paraphrased from an email from a Southwest pilot.

Further, the pilot argues that Southwest has more flexibility from the coronavirus vaccine mandate than it described.

Previously, the pilots’ labor union slammed the vaccine mandate.

“This announcement and lack of detail only fuels a growing divide that continues to erode the already strained relationship between Southwest Airlines and its Pilots’ Union,” SWAPA said in a statement. “Despite current CDC guidelines, SWAPA has not had any meaningful conversation with management about levels of antibodies, natural immunity, or any other type of qualified exemptions.”

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Cooper Moran is a reporter for The Star News Network. Follow Cooper on Twitter. Email tips to [email protected].