This is an interesting question.
Pretty much every US and European airline hates this plan, as does any labor group worth its salt. The airlines obviously don’t like the idea of competition with a cost advantage, and the labor groups don’t like the idea of cheap labor undermining their efforts. The argument being put forth is that Norwegian is trying to create a “flag of convenience” operation – a company that bases itself wherever it wants to circumvent less favorable laws. Is that what Norwegian is trying to do here?
Norwegian is attempting to offer low-cost on transatlantic flights—a nut that no one has truly cracked. As the author states, not everyone is happy, certainly not the competition.
I understand the open question about the flag (though it's an habit for maritime transport for instance), but it's not as if Norwegian went to some exotic country, just another EU country (basically, one subsidiary operates the planes, one other owns the routes and the mother company sits in Norway).
In the end, as long as the company is in line with the law, denying a flight permit is an overreach.