I don't see how they risk your jobs more than even lower paying european carriers. Like for example Air Serbia, Open Skies, LOT and so on. Remember, the open skies agreement gives every EU carrier pretty much unrestricted traffic rights into the US, however, unlike for US carriers in the EU, no intra-US traffic rights.
Of course their flag of convenience scheme is directly threatening european carriers, but those do not picket their LGW base or any other base for that matter. After all, NAI as a part of the Norwegian group is just a latecomer to the market, the T&Cs have been already destroyed by the likes of Ryanair, Wizzair und in some parts Easyjet, not to mention pure pay to fly airlines like Air Baltic (which could fly that way into the US tomorrow if they want to).