New court filings from a coalition of aviation unions in the US have appealed against the US Department of Transportation's decision to allow Norweigan Air to operate flights between the US and Ireland.

They say the decision "systematically violated virtually every basic rule of treaty interpretation" in the US.

Union's have argued that Norwegian is trying to avoid the US's tougher labour rules by setting up an Irish subsidiary to employ low-paid crew, this claim has consistently been denied by the airline.

They argue that the department's ruling misrepresented details of existing Open Skies agreements and failed to include a public interest evaluation.

Last year, Democratic challenger for the US Presidency, Bernie Sanders, registered his opposition to the granting of Norweigan Air's permit.

"We must do everything we can to prevent a global race to the bottom in the airline industry. If this permit is approved, it would open the door to the same 'flag of convenience' model that decimated US shipping," he said in a letter to the US Department of Transportation.

Reaction

A spokesperson for the airline said, "These are tired and false allegations already dismissed by the Department of Transportation's order last year."

"Opponents claim that Ireland is simply a 'flag of convenience'. In reality, NAI is headquartered in Dublin with 80 employees, 37 aircraft registered in Ireland, and already operates flights to and from Ireland, with many more routes planned," the company previously commented.

From July, Norwegian will launch a series of new low-cost transatlantic routes from Cork, Shannon and Dublin. The flights will serve smaller airports on the US east coast offering access to the New York, Boston and New England areas.

Its fares begin at €69 each way.