The seatbelts can't be extended because of the airbag mechanism, according to the Post.
The airline has now imposed a waist size limit on passengers and banned passengers carrying infants on their laps.
And it isn't the first airline to take aim at overweight passengers.
European airline Finnair announced plans in November to weigh passengers before they boarded a plane.
The Finnish airline said it wasn't doing it to penalise passengers for being overweight, but merely to cut down on operating costs. By working out a more exact weight and balance of the aircraft, Finnair said it could streamline the cost of fuelling its planes.
Samoa Air became the first airline in the world to charge passengers based on weight in 2013.
The airline, which now no longer operates, asked passengers for the local equivalent of 50 cents for each kilogram they were bringing on board — both on their body and in their suitcase.
And in a controversial policy introduced in 2016, Hawaiian Airlines said passengers flying out of American Samoa could no longer preselect their seats, with staff to eyeball heavier passengers instead and seat them in a way that more evenly distributed weight on board.
But the airline rubbished claims it was weighing passengers at American Samoa's Pago Pago International Airport.
In a survey of UK passengers in November, four out of five people said they wanted overweight passengers to sit in special zones on the plane that offered wider seats, bigger aisles and more leg room.
The strong views came from research by UK travel website Jetcost, which saw one in 10 passengers saying they had endured an uncomfortable flight because the passenger sat next to them was overweight.
Thai Airways fitted the new seatbelt airbags on business class seats on its Dreamliner 787-9 fleet. The airline added two new Dreamliners to its fleet in September.
