A pilot with Southwest Airlines was cited for assault and battery after an alleged physical altercation with a flight attendant over wearing a mask, according to USA Today. The Oct. 18 incident occurred at a California hotel bar, where the crew was spending the night after a flight. A public information officer with the San Jose Police Department declined to provide details, but confirmed “the event involved a disagreement over mask-wearing or masks.” The pilot has been placed on leave while the “crew disagreement,” as an airline spokesperson put it, is reviewed by the Santa Clara County District Attorney’s office for possible charges.

Four days after the incident, Southwest executives circulated a memo to employees, warning that “crossing the line in a heated conversation can be a violation of our guidelines for employees and can even end in loss of job.” It chided pilots and attendants about “the Golden Rule,” saying that it “is vital that we treat everyone with respect and honor our differences without pushing our ideals on someone else.” On Sunday, the airline announced it would be launching an investigation into the circumstances surrounding a pilot allegedly invoking a right-wing catchphrase during an inflight announcement.