A Southwest pilot and flight attendant fought over masks. One was cited for alleged assault.

A Southwest Airlines pilot was cited for alleged assault and battery after a mask dispute with a flight attendant at a California hotel amid pandemic political discord at the nation's largest domestic carrier.

The incident happened Oct. 18 at a hotel bar in San Jose, California, where the crew spent the night after a flight, according to police records and company and union officials.

The case has been referred to the Santa Clara County District Attorney's Office for review and possible charges, according to Sgt. Christian Camarillo, public information officer for the San Jose Police Department.

"The event involved a disagreement over mask wearing or masks," Camarillo said, declining to provide more details.

The district attorney's office is reviewing the case, according to spokesman Sean Webby.

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Southwest placed the pilot on leave while the matter is investigated, airline spokesperson Brandy King told USA TODAY.

King confirmed there was a "crew disagreement during an overnight trip."

"We do not have information to provide regarding the context of the event, and we do not discuss personnel issues externally," King said.

The San Jose incident happened on a Monday night. That Friday, Oct. 22, Southwest sent a lengthy memo to pilots and flight attendants about civility and the golden rule. "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 said.

"We realize there has been a steady drumbeat over the last 19 months about civility and respectful discourse – and that is for good reason. Many of our people have been faced with an uncomfortable situation where their beliefs are not shared by someone else, resulting in a confrontation of some kind," the memo began. "And for every situation we hear about, there are dozens more for which we don't. It is vital that we treat everyone with respect and honor our differences without pushing our ideals on someone else."

The memo sent by Bob Waltz, Southwest's vice president of flight operations and Sonya Lacore, vice president of inflight operations, recommends that flight crews have a briefing at the start of a trip to "set the right tone" about concerns and expectations. It reminds employees masks are required, including during briefings.

"And when the day is done and we retire for the day/evening, it is especially important that we measure our discussions when they veer toward sensitive topics that elicit emotional responses," the memo said. "Being off-duty is never an excuse to ignore the Golden Rule. Everyone has a different story before coming to work, and many times the best support we have is one another."

Southwest's flight attendants union, TWU Local 556, said in a statement, "We are aware of this matter and the fact that the investigation continues. As with all flight attendants we represent, we will support our member in accordance with the law and our collective bargaining agreement.''

The Southwest Airlines Pilots Association, which represents the airline's pilots, declined to comment, citing the pending investigation.

This article originally appeared on USA TODAY: Southwest Airlines pilot cited for assault, battery after mask dispute