A Southwest Airlines pilot is being investigated for allegedly assaulting a flight attendant at a San Jose bar last month after the two argued over face masks. The Santa Clara County District Attorney’s Office is in the process or determining whether criminal charges should be filed against the pilot, who was not named.

Southwest says the pilot has been placed on leave while the investigation is ongoing.

Southwest’s pilot union has been outspoken against the company’s mask and vaccine mandates. Initially, Southwest said staff that weren’t vaccinated by Dec. 8 would be put on unpaid leave, but scrapped those plans on Oct. 19, the day after the incident in San Jose.

Southwest has had a run of bad luck this year. Last month it canceled 1,000 flights over one weekend, blaming “disruptive weather” (though no other carriers saw similar delays). The union, at the time, said the issues were not due to any official or unofficial job action.

In May, a Southwest Airlines flight attendant was attacked by a passenger and lost two teeth in the incident, according to a letter from the flight attendant’s union to the carrier’s CEO. And in January, another Southwest passenger who was asked to leave a flight after refusing to wear a mask “called each of the two flight attendants ‘pathetic,’ and hit one of the flight attendants with his bags.” He was fined $16,500.

Southwest has also warned of forthcoming flight schedule cuts, saying in August that it continued to struggle with staffing issues and was attempting to better align its employee operations.

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