The laws in the US are probably very different than those in Norway when it comes to job action in the transportation industry. Also, if the WestAir mentioned is the Irish one, this also applies.
US law, the Railway Labor Act (often referred to as the RLA), has very strict guidelines and time tables for "self help", or job actions, in the transportation industry. It is difficult if not impossible for labor at a medium size or larger airline to coordinate a sick out without some type of trail, either written (email, web postings), or verbal. Company management can present these items to a judge and get some hefty fines against unions (again, my previous reference to AMR and CMR); they can also use this to legally terminate pilots. I don't know of it is true, but I heard that DAL tried to do this to some pilots in 2000-2001 toward the end contract negotiations when some pilots suggested write-up campaigns, not picking up open time (again, if this is coordinated it is considered an illegal job action), or sick outs.
Unfortunately this plays into the hands of management. They can and do drag out negotiations for years with no fear of labor action.
For any new hire at a US airline, if you are not familiar with the RLA get with a union rep and find out about the nuts and bolts of it. Again, even TALKING about a job action in a crew lounge, or posting something on a union website can lead to termination and the union will NOT be able to help.