More than 350 flights were grounded by Southwest Airlines on Monday following days of disrupted operations which were reportedly caused due to issues with the air traffic control and bad weather.

The aviation giant previously said that the situation would be a minor speedbump, however, the pilots union said the company has been providing a botched response.

Monday marked the third consecutive day of mass flight cancellations, which have left large numbers of passengers stranded.

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The cancellations on Monday amounted to 10% of Southwest’s schedule, and at least 1,400 other flights, or roughly 40%, were delayed, according to the reports from Associated Press citing the FlightAware tracking service. Shares of Southwest Airlines Co. fell 4.2% on the day.

On the second day of flight call-offs, hundreds of flights were cancelled in the United States on Sunday, leaving passengers to scramble on a three-day holiday weekend.

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As of 2 pm EDT, Southwest Airlines cancelled over 1,000 flights, or 28% of its schedule, which was the highest rate by far of the major US airlines. Allegiant and Spirit airlines cancelled 5% and 4% of its flights respectively while American Airlines canceled 2% of its flights.  

The disruptions in the flight schedule of Southwest Airlines was was shaken after a pilot’s union, which has nearly 9,000 members, appealed to a US federal court to dismiss COVID vaccination orders. 

The Southwest Airlines Pilots Association said that the company must be open to negotiating the terms as vaccinations could involve sick leave or disability if pilots have a reaction to the vaccine.

“We are not anti-vaccination at all, but our pilots are extremely worried about how their medicals are going to be handled” if they are unable to fly, union president Casey Murray said in a statement.

(With AP inputs)