A United Airlines Dreamliner flight bound for Tel Aviv returned to New York late last week after two passengers awarded themselves a business class upgrade then refused to return to their correct seats after the crew asked them to do so.

Business class upgrade goes awry for two United passengers

The flight, UA90, was last Thursday's late-night departure from New York's Newark Airport heading to Tel Aviv. According to multiple media reports, the Boeing 787-10 was tracking northeast towards the US Canadian border when the pilots decided to turn around due to the disruptive passengers.

UA90 pushed back at Newark just after 23:00 on Thursday with 123 passengers and 11 crew onboard. Around 90 minutes into the flight, two Israeli passengers decided to bump themselves up from the main cabin accommodations to the more salubrious confines of business class.

When the crew asked the two passengers to show them their tickets, the passengers refused. Here's where the situation gets murky. In a statement, United Airlines alleges the two passengers were disruptive. A passenger onboard told Israeli media "a riot started."

Other sources say the flight attendants asked the two passengers several times to return to their correct seats, but the passengers refused. There are also reports of loud arguments.

"Some commotion started on the plane between two passengers and flight attendants," passengerRoi Lotan told Israeli media."It was a half-empty flight, and there was room, so they probably said to themselves, 'why not?'"

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Zero tolerance regime for disruptive passengers

There's some uncertainty surrounding exactly how disruptive the two passengers were. But what is crystal clear is that the pilots wasted no time turning the aircraft around.

This decision could reflect a zero-tolerance for any unruly inflight behavior rather than the actual seriousness of the disruption. Frontline aircraft employees, including flight crews, have worked hard over the last year or two to shine a spotlight on bad passenger behavior.

Just two hours after departure, UA90 was back on the ground at Newark, where Port Authority of New York and New Jersey police boarded the plane. CNN, citing the Port Authority Police Department, is reporting no charges were laid.

Unfortunately, for the rest of the passengers, United Airlines canceled the flight. However, the airline did come to the party by providing meal vouchers and hotel accommodation until the airline arranged alternative flights.

FAA warns of criminal prosecutions and fines

Obnoxious passengers are nothing new for airlines. But US airlines have campaigned hard in recent years to raise awareness of the issue. Last year, the FAA received 5,981 reports of unruly passenger behavior after imposing a zero-tolerance order early last year.

The spike in reports reflects both the zero-tolerance policy and a raft of new travel rules, including wearing face-masks inflight. The FAA received 4.290 reports of mask-related incidents from airlines last year.

Last June, United Airlines joined a consortium of other US-based airlines to ask US Attorney General Merrick Garland to step up prosecutions of disruptive and violent passengers.

The FAA says repercussions for passengers who engage in unruly behavior can be substantial. The FAA can issue fines or initiate a criminal prosecution.