A Southwest Airlines pilot is under investigation for allegedly assaulting a flight attendant at a California bar during an argument over wearing masks, authorities said.

The pilot was cited for assault and battery in connection with the Oct. 18 dispute at a hotel bar in San Jose, USA Today reported Tuesday. The airline told CBS News the employee in question is currently on leave.

“Last month we received a report of a crew disagreement that occurred while off duty on an overnight trip,” the airline told CBS News in a press release. “We are conducting an internal investigation which will include any results of the charges that have been filed with local authorities.”

The Santa Clara County District Attorney’s Office is reviewing the incident to determine whether criminal charges should be filed, the San Jose Police Sgt. Christian Camarillo told USA Today.

The name of the pilot was not disclosed.

The incident comes amid a wave of unruly air passengers this year, who sometimes become violent.

Airlines reported about 3,000 cases of disruptive passengers between Jan. 1 and mid-June, according to the Federal Aviation Administration, which began tracking it this year. About 2,300 of these incidents involved passengers who refused to obey the federal requirement to wear a face mask.

The hotel bar incident “involved a disagreement over wearing masks or masks,” Camarillo told USA Today, declining to provide further details.

USA Today reported that a few days after the incident, Southwest sent a note to pilots and flight attendants warning them that, “Crossing the line in a heated conversation may be a violation of our guidelines for employees and may even result in a job loss. “

The flight attendants union TWU Local 556 told CBS News it was aware of the incident:

“As with all flight attendants we represent, we will support our member in accordance with the law and our collective agreement,” the union said.