The airline blamed air traffic control issues and weather in Florida on Friday, saying the ripple effects put planes and employees out of place, and it had too few reserves [!] to pick up the slack....Southwest and its pilots union have steadfastly denied that workers walked off the job to protest a federal vaccine mandate. (The pilots sued the airline to stop the mandate.)

"The fact is the Florida weather on Friday and unexpected ATC issues on Friday night resulted in delays and cancellations across our network, and it just got us behind."
[...]
"They were just caught in a perfect storm," [Jon Jager aviation analyst] said, citing staffing levels [!], weather and flight crews running out of time because of the delays and cancellations. Pilots and flight attendants are only allowed to work a certain number of hours per day due to [union] contract[s] and government rules.

U.S. Northern District Justice David Hurd of Utica granted a preliminary injunction temporarily barring New York state and employers from enforcing the COVID-19 vaccine mandate against medical workers claiming a ["]legitimate religious exemption["]. Last month, Hurd issued a temporary restraining order blocking enforcement of the mandate in relation to ["]religious beliefs["].

Southwest Airlines and American Airlines are among the carriers that are federal contractors and subject to a Biden administration requirement that their employees are vaccinated against Covid-19 by Dec. 8 unless they are exempt for medical or religious reasons.
[...]
Southwest's senior vice president of operations and hospitality, Steve Goldberg, and Julie Weber, vice president and chief people officer, wrote to staff on Friday that if employees' requests for an exemption haven't been approved by Dec. 8, they could continue to work while following mask and distancing guidelines until the request has been reviewed.