Airline passengers are getting angrier and harder to manage, according to a new letter from the union president representing Southwest Airlines flight attendants. The union is asking for more air marshal presence onboard flights, and for more passengers to be banned entirely.

The letter stemmed from a Sunday incident on a flight from Sacramento to San Diego. As the Associated Press reports, a female passenger allegedly refused to comply with instructions from a flight attendant, and became unruly, ultimately knocking out two of the flight attendant's teeth.

A spokesperson for Southwest tells the AP that the passenger "repeatedly ignored standard inflight instructions and became verbally and physically abusive upon landing." She was reportedly taken into police custody in San Diego.

Lyn Montgomery, the president of Local 556, the flight attendants' union, noted in a letter to Southwest CEO Gary Kelly that this is far from an isolated incident, and standard training to de-escalate situations with angry passengers is no longer sufficient. Just between April 8 and May 15 there were a reported 477 incidents of passenger "misconduct" on Southwest alone. Since the beginning of the year, the FAA has had 2,500 reports about misbehaving passengers, 1,900 of which stemmed from refusing to wear face masks.

"I’ve been in the industry since 1992, and this is the worst ever," Montgomery said, speaking to the AP. "People seem to be more angry. When they’re asked to do something, compliance seems to be more difficult."

Montgomery's letter, she said, was a plea for help in ending "travesties" like the Sunday incident. She said that "passenger non-compliance events" have reached an "intolerable level," and had generally become "more aggressive in nature."

She also expressed apprehension about the return of alcohol service, which has been temporarily suspended aboard Southwest flights.

Last week, a JetBlue flight from New York to San Francisco was diverted to Minnesota due to an unruly, apparently intoxicated passenger.

"It must be noted that Southwest Flight Attendants are doing all they can do to ensure compliance while creating a safe environment for all passengers and crew," Montgomery wrote. "But they also need the support and tools required to prevent injury to ourselves and others."

Among the tools she requested is more use of Southwest's restricted passenger list — she claimed that some misbehaving passengers were simply put on different flights. Also, she requested that Kelly lobby federal officials to get more air marshals assigned to Southwest flights, so that they may intervene in these situations.

Related: JetBlue Flight Bound for SFO Gets Diverted Due to Unruly, Drug-Snorting Passenger