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(NEXSTAR) – A union representing thousands of Southwest Airlines flight attendants is demanding the CEO take action to better protect the carrier’s crew from unruly and violent passengers.

Lyn Montgomery, the president of TWU Local 556, outlined some of the disruptive behavior in a letter to Southwest CEO Gary C. Kelly on Monday, including one incident that resulted in a flight attendant suffering facial injuries and the loss of two teeth.

Southwest Airlines has since confirmed an incident on Sunday morning, during which a passenger repeatedly ignored the crew’s instructions and became physically abusive.

“This unprecedented number of incidents has reached an intolerable level, with passenger non-compliance events also becoming more aggressive in nature,” wrote Montgomery.

“Unfortunately, this is just one of many occurrences,” she added. “I write to you today because we cannot tolerate our beloved Cohearts being abused in such a manner, and because I am asking for your help and leadership in ending these travesties.”

On behalf of the union, which represents over 15,000 Southwest flight attendants, Montgomery made several demands of Kelly, including the need for Southwest to publicly denounce bad behavior and clearly outline the “consequences” to customers, which can range from civil penalties to criminal charges and possible jail time. She further urged Kelly to demand the government increase the number of Federal Air Marshals in the skies.  

Montgomery also said Southwest should “better utilize” its restricted traveler list for unruly passengers, including those that defy federal mask mandates.

“No passenger should be removed from one flight only to be permitted to board the very next Southwest Airlines flight after a non-compliance incident. We ask that you take a strong stance to ensure that unruly passengers are not welcome to travel with us, period, full stop,” she wrote.

These steps, Montgomery said, were necessary now more than ever, as in-flight alcohol sales are resumed amid an “already volatile environment.”

In response to the union’s letter, a spokesperson for Southwest issued a statement confirming one incident of physical assault on Flight 700 from Sacramento to San Diego on Sunday morning. The statement also briefly reiterated Southwest’s stance on unruly passengers but did not address Montgomery’s demands specifically.

“We do not condone or tolerate verbal or physical abuse of our Flight Crews, who are responsible for the safety of our passengers,” the statement read.

The FAA had also publicly acknowledged a “disturbing increase” in violent or disruptive behavior as far back as January, when the agency announced its zero-tolerance policy for unruly passengers. The FAA specifically noted a “proliferation” of such conduct stemming from passengers’ refusal to wear masks, and “following the January 6, 2021 violence at the U.S. Capitol,” according to an order signed by FAA Chief Steve Dickson.

Earlier this month, the FAA also confirmed that U.S. airlines had reported  1,300 incidents of unruly passengers since February. TWU Local 556 claims Southwest’s flight attendants were forced to deal with “477 passenger misconduct incidents” during a five-week span in April and May alone.