The new fares are being introduced on London long-haul routes and offer reductions of up to £60 on economy tickets for customers willing to be allocated a seat and take only hand luggage.
However, five of the 10 routes to be affected are also operated by low cost carrier Norwegian out of Gatwick, while on three of those, they are the only two airlines offering them so putting them in direct competition.
A Norwegian spokesman said: "We’re flattered competitors are just starting to see the importance in giving consumers lower fares and the flexibility to choose what they need.
"We welcome competition and continue to fly passengers in modern state-of-the-art aircraft on nonstop flights from London Gatwick."
He added destinations included Austin, Denver and Singapore with one-way prices leading in at £160, £175 and £160 respectively.