(KTLA) – A female flight attendant suffered a broken nose after being punched in the face repeatedly during a flight from New York City to California that made an unscheduled landing in Denver Wednesday.

Some witnesses on the plane alleged that the incident began when the passenger became upset over having to wear a face covering. However, American Airlines said they have “no information suggesting the incident was mask compliance-related.”

Witnesses who were on the plane told KTLA that alcohol was also involved before things turned violent.

“Halfway through the flight, all of the lights came on and the captain asked for two able-bodied men to come to the front, which automatically is alarming,” passenger Mackenzie Rose said.

The captain then said they would be making an emergency landing in Denver. The man had to be duct-taped to his seat, passengers said.

“Based off of what the flight attendant said, she said that the flight attendant was punched in the face, twice, and her nose was broken so she needed to get off and go to a hospital, and the police needed to get on and arrest the man,” Rose said.

Paul Hartshorn Jr. of the Association of Professional Flight Attendants confirmed the flight attendant’s injuries in a Thursday statement and added that she has since been released from the Denver hospital and is on her way home.

“After a flight attendant who was working in a different cabin bumped this passenger, we’re told, she then walked into one of the flight galleys and this passenger approached her and punched her in the face at least twice. That’s what we know right now and she sustained broken bones in her nose and her face,” Hartshorn said.

After Flight 976 landed in Denver, the passenger, who was not identified by the airline, was “removed and apprehended” by law enforcement, according to American Airlines.

“We are outraged by the reports of what took place on board,” a statement from the airline said. “Acts of violence against our team members will not be tolerated by American Airlines. We have engaged local law enforcement and the FBI and we are working with them to ensure they have all the information they need.”

The airline added that the passenger involved in the altercation “will never be allowed to travel with American Airlines in the future, but we will not be satisfied until he has been prosecuted to the full extent of the law.”

An FBI spokesperson told KTLA that no arrests have been made as of Thursday afternoon but the investigation is ongoing.

Hartshorn, of the Association of Professional Flight Attendants, called for a national no-fly list “that encompasses all airlines.”

“APFA, on every level, will be supporting the crew involved in this incident to ensure the FBI has all the information they need to proceed with prosecution,” Hartshorn said. “This is another outrageous attack on Flight Attendants. Please continue to maintain situational awareness, remain vigilant, and attempt to deal with all safety and security issues on the ground.”

Reports of unruly behavior on planes, including violence against crew members, have increased since the start of the pandemic. The FAA says 923 investigations have been initiated this year into violations of regulations or federal laws. The number is up from 183 last year and 146 in 2019.

“This behavior must stop, and aggressive enforcement and prosecution of the law is the best deterrent,” American Airlines said.

The FAA has been handing out hefty fines this year after a surge in these unruly passenger incidents, most of which are over mask mandates.

Assaulting a flight attendant is a felony and could land the offender up to 20 years in prison.

American Airlines said both the FAA and the FBI will actively investigate the matter.

The airline also expressed support for the employee who was attacked.

“We thank our crew for their quick action and professionalism to ensure the safety of their fellow team members and customers on board,” the statement reads. “Our thoughts are with our injured flight attendant and ensuring that she and her fellow crew members have the support they need at this time.”