Norwegian has been using contractors for a long time, thereby avoiding tax and social responsibility. Guess an investigation is about to begin there as well? ...or is Kjos, the national hero, able to avoid such a thing?
See there's a difference between being a contractor, and having a non-permanent employment contract.
To my knowledge, the 6-month contracts Norwegian issue are 6-months
employment contracts. Even though the length of employment is given (ie it's non-permanent), it is still employment, and of course the employer would have to answer for social responsibilities.
Might not be ideal for a pilot (as opposed to full-time indefinite employment), but it's fair - you know what you get, you might have certain rights if positions open at the end of a contract, it's legal, and you run no personal risk of (involuntary) tax fraud.
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Edit: a litte quick there, see posts below