Obese passengers and parents travelling with children have been booted back to economy class by Thai Airways because the new seat belts won't fit their waistlines, wrote dailymail.co.uk.

The international carrier banned kids and overweight people from flying business class after adding two new Dreamliner jets to their fleet in September last year.

The airline said customers whose waistlines exceeded 142cm would not be able to fly the premium service because of the new seat belt airbags.

Thai Airways said if passengers can't fasten their seat belt it would be breaking U.S. safety standards. 

The airline also said the seat belt can't be extended because of the airbag feature, introduced to protect the passengers.

The new feature means parents who intended to carry toddlers on their lap can't sit on the new seat on the Boeing 787-9 'dream liner' aircraft.

Thai Airways isn't the first airline to take this step with weight restrictions on their customers.

Finnair last year started to weigh their customers a head of boarding the plane. 

They conducted their own survey with 2000 willing customers so they could get a more accurate estimate on how much they would be able to streamline their operating costs. 

According to the European Aviation Safety Agency the average weight of a female passenger is 64kg and for a male it is at 84kgs. 

Last year Jetstar passengers began to charge parents an extra $30 to $50 to carry their children on their lap.