Wizz Air and Ryanair, 2 of Europe's biggest airlines, are in a war of words over Wizz's divisive new 'all you can fly' deal

• Ryanair's CEO criticized Wizz Air's unlimited flights pass as a "marketing scam."
• He said the flights could sell out before pass holders had a chance to book them.

Tensions are growing between two of Europe's top budget airlines after the Ryanair CEO called Wizz Air's unlimited flights pass a "marketing scam."

Wizz Air launched its "All You Can Fly" pass last week. For 499 euros ($550), customers could take as many flights as they wanted for a year.

The Budapest-based carrier flies as far as Dubai and the Maldives.

The pass proved popular too, with all 10,000 selling out within 48 hours, per Bloomberg. The report added that Wizz is considering releasing more.

However, the unlimited-flight pass also comes with several caveats.

For example, there's a flat fee of 9.99 euros ($11) to be paid separately for each flight segment. Plus, you can only book a flight up to 72 hours in advance.

Michael O'Leary, CEO of Ryanair, is among its critics.

"It's a bit of a marketing scam," he told Irish radio station Newstalk.

O'Leary said that because booking opens 72 hours in advance, "most of the flights will be full — there'll be no seat availability."

"It's an interesting marketing stunt, but that's all it is," he added.

Wizz Air's chief corporate officer, Yvonne Moynihan, later spoke to the same radio station.

"The comments of Mr. O'Leary were not only provocative but they were also inaccurate," she said.

Moynihan said it "wouldn't be very likely" that a flight would sell out 72 hours in advance. She added that Wizz Air flights have an average load factor between 90% and 95%.