Southwest Airlines announced their compliance with President Joe Biden’s vaccine mandate on October 4. However, the weekend of October 9-11 has seen more than 2,000 flight cancellations and more than 3,000 delayed flights in response to the company’s edict. Southwest employees have until December 8 to submit to the COVID-19 vaccine or be let go, according to the airline.

Currently, Southwest denies that pilots have called in sick to protest, instead claiming weather delays are to blame and that the FAA experienced staffing issues with air traffic controllers on Friday, October 8. However, in a statement to Fox Business, the FAA denied weekend delays and claimed that any issues with the staffing of air traffic controllers had been sorted by Friday evening.

Notably, despite the claims of weather delays and FAA staffing issues, no other airline had as many cancellations or delays this weekend.

The Southwest Airlines Pilots Association also denied any collective action taken in protest on Saturday, stating, “SWAPA is aware of operational difficulties affecting Southwest Airlines today due to a number of issues, but we can say with confidence that our Pilots are not participating in any official or unofficial job actions.” SWAPA took a jab at Southwest Airlines, saying, “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.”

SWAPA, however, would be unable to comment any differently because pilots are prohibited under federal law from any organized strike that would withhold labor.

Despite the consistent denials regarding the reasons for the cancellations and delays, many pilots are individually confirming to reporters and friends that the cancellations and delays are indeed due to walk-out protests.

In a tweet late Sunday evening, U.S. Sen. Ted Cruz insinuated the walk-out occurred due to the vaccine mandate, stating, “Joe Biden’s illegal vaccine mandate at work! Suddenly, we’re short on pilots & air traffic controllers.”

SWAPA had already filed a lawsuit requesting a temporary injunction to halt the mandate until negotiations have been completed between the airline and the union. This case, Southwest Airlines Pilots Association v. Southwest Airlines Co., will be heard in the U.S. District Court of the Northern District of Texas (Dallas). SWAPA is also seeking additional coverage for employees in case of vaccine injury, which has not been addressed by Southwest Airlines. Pilots must undergo a physical every year, and if vaccine injury occurs and the pilot cannot pass the physical, then the pilot loses their ability to fly—as well as their livelihood.