Norwegian Air International (NAI) has been granted approval to begin flights between Ireland and the US after a three-year process in which the US Department of Transportation (DOT) seemed reluctant to give the go-ahead despite being unable to find any legal reason to reject the application.

In a dramatic turnaround Dec. 2, DOT announced it was granting NAI a foreign air permit. The announcement came just days after the European Commission said it would take the US to court over the application delay.

Low cost carrier NAI, an Irish unit of Norwegian Air Shuttle, is seeking initially to fly from Cork, Ireland, to Boston and later from Cork to New York. The application falls within the remit of the US-European Union Open Skies agreement, but labor groups and some US airlines have fiercely opposed it. The Air Line Pilots Association International (ALPA) alleges NAI is operating under a flag of convenience and that allowing it to operate in the transatlantic market threatens US pilot jobs.

DOT granted NAI tentative approval in April, but left the application hanging through the rest of this year, prompting sharp criticism from the EC.

“This case is among the most novel and complex ever undertaken by the Department,” DOT said in a statement. “We have taken the necessary amount of time to review and consider the comments from a wide range of stakeholders. Regardless of our appreciation of the public policy arguments raised by opponents, we have been advised that the law and our bilateral obligations leave no avenue to reject this application. We find that the clear weight of legal analysis in this case directs us to uphold the tentative findings and conclusions previously made.”