(Reuters) – Southwest Airlines (NYSE:) Co cancelled at least 30% of its scheduled flights on Sunday, a second straight day of heavy cancellations, data from flightaware.com https://flightaware.com/live/cancelled showed.

Southwest did not confirm how many flights were cancelled. It stated that the cancellations occurred due to bad weather in Florida, and was further complicated by issues with air traffic control.

In an emailed statement, the airline stated that recovering from operational problems is harder and more time-consuming because there are fewer flights between cities on our schedule.

Flight tracking website shows that the airline cancelled 1,103 flights Sunday so far. That’s on top 808 cancellations on Saturday, representing 24%. It was significantly higher than other airlines’ cancellation rates.

Southwest Airlines pilots union denies speculations that cancellations are due to union action. On Oct. 5, the union announced that it would file temporary restraining orders to prevent Southwest from complying with a COVID-19 vaccination mandate for federal contractors. This includes major airlines.

The union, SWAPA, put out a statement https://www.swapa.org/news/2021/press-release on Saturday saying it was “aware of operational difficulties affecting Southwest Airlines” but that its pilots were “not participating in any official or unofficial job actions.”

Southwest’s vice president for daily operations Alan Kasher stated earlier that employees were not aware of the magnitude of the disruptions.

“And as we’ve seen before, an unexpected number of delays ultimately leads to a staffing shortage, and at times, mandatory overtime because of the longer operating day. Although we’ve made schedule adjustments leading into the fall, our route system has not fully recovered—that will take time,” he wrote on the company’s intranet.

Federal Aviation Authority stated that there had not been any shortages in air traffic personnel since Friday, but noted that certain airlines faced scheduling difficulties due to out-of-control aircraft or crews.