A battle is brewing over the lucrative trans-Atlantic routes that have been dominated by major U.S. and European airlines.

Upstart Norwegian Air Shuttle is ruffling rivals’ feathers with its plans to bring the kind of low-fare service offered domestically by Southwest and JetBlue to flights across the Atlantic.

Norwegian is the third-largest low-fare airline in Europe.

The loudest complaints are coming from airline employee unions, which contend that Norwegian is trying to skirt labor laws by establishing operations in Ireland and hiring pilots out of Asia.

The Airline Pilots Association International and the Association of Flight Attendants have petitioned the U.S. Department of Transportation to refuse to accept Norwegian flights out of Ireland. Delta, United and American Airlines also oppose the move.

Norwegian Air Shuttle already offers flights from the U.S. to Europe at up to $150 to $500 cheaper than its U.S.-based competitors. But critics say the move to operate a long-haul company out of Ireland would let Norwegian take advantage of more lenient labor laws to undercut rivals by even more.

“Do you really want your airline going around the law to employ pilots out of Bangkok?” said Michael Robbins, a spokesman for the Airline Pilots Association. “Is that what the American consumers want?”

Norwegian Air Shuttle rejects such contentions, saying it will abide by the labor laws of every country in which it operates. The airline says critics are just trying to keep out low-fare competitors.