A 16-year-old spent his Oslo to New York flight freezing since he only had cash and no credit card with him to pay the $5 fee charged by the carrier for renting a blanket, the daily newspaper Aftenposten wrote.
That followed a report last week of Norwegian crew members taking back a cup of coffee from a Thai woman after it emerged she only had cash and a local credit card with her. The woman was also unable to buy food or water on the 12-hour flight.
"This is totally unacceptable. Norwegian must ensure its passengers are treated well and we apologize deeply," company spokesman Lasse Sandaker-Nielsen told AFP.
"We are the first to admit that we have had some start-up problems on the long-haul flights," he told AFP.
Only a handful of budget airlines operate long-haul routes and passengers are sometimes surprised to find out that they have to pay for services other carriers offer free of charge.
Norwegian is going to review its policy of only accepting credit card payments and will improve its communication with customers, Sandaker-Nielsen said.
The two episodes quickly drew the ire of social media users.
"Unbelievable that people have the courage to fly Norwegian. Not being able to drink water can lead to death," said Thor Olsen on Twitter, while Tor Andre Ljosland speculated that "soon you will also need a credit card to use the toilet."
Norwegian expects to take delivery of its first Boeing 787 Dreamliner at the end of this month, almost two months behind schedule following problems with the planes' batteries.
The company has leased two Airbus A340s from Portugal's HiFly to avoid delaying the launch of its New York and Bangkok flights.