If you go to Norwegian Airlines, your chances of ever flying for an airline represented by ALPA will be slim to nil.
The trade unions have a tremendous influence with the companies over who who is eligible to be hired.
There's some truth to the above, but:
1. Blackballing pilots simply because they worked at a non-union airline is highly illegal
2. Not so long ago, a new US regional airline was setup specifically to circumvent a union CBA and there was a lot of resentment from other pilots and talk of union blacklisting. But in reality, pilots from this regional flowed to
all of the majors just fine.
3. At many airlines, the hiring pilots are management (non-union) pilots anyway. They have seats to fill and don't care about union politics.
I think there's real resentment out there but some of the rhetoric are way overstated.