... I do agree that a company shall respect seniority - I the case with Norwegian the picture is a bit different ....
NAS (Norwegian Air Shuttle) was a purely Fokker 50 operation until a few years back. The decision to start a new "wing", a low price competitor to SAS was taken, and to operate 737's. There was no Union in the 737-operation - only in the F50 operation. The F50 operation ceased and all F50 pilots was transferred and given type's. Several of the commanders did not pass their skills test. Only after restesting 2 or sometimes 3 times did they pass.
Now - Norwegian has expended strongly after this took place and the number of suitable right-seaters are dwindling - down to 5 or 6 as far as I know. They are unable to fill the 12 positions needed.
It is in this case that it would be suitable to let "outsiders/new-hires" with type and experience fly right seat 2-300 hours to get to know the operation and "the specialities" in the norwegian met-conditions along the more than 2500 km coast. And THEN break seniority to fill a left seat position .....
Or am I totally wrong ... again ....