A little clarification for the those without a lot of airline experience...
This sort of grass-roots job action (sick-outs, slow-downs) is technically illegal and IS NOT protected labor activity at any union or non-union airline. A real honest-to-goodness strike has to be authorized in advance by the federal government, after years (and I do mean YEARS) of attempted negotiation.
Employees participating in this sort of thing can be fired by a union or non-union company...however the company would have trouble proving that you weren't really sick, so the chances of anyone getting fired are slim.
More likely the company would attempt to identify the ring-leaders, and fire or sue them...yes, the company can sue and will win for economic damages due to an unauthorized labor action.
Actually union work groups are at a SERIOUS disadvantage in this sort of situation. A non-union company would have trouble pinning down the correct people to sue, and even if they did all they would get would be what they own personally. At a union company the company would just sue the union...the courts generally hold that the union is responsible even if it cannot be proved that they instigated it. The assumption is that that the MEC could have and should have stopped it. The company will get a massive judgement (millions, or tens or even hundreds of millions), which the union will have to pay...this means the PILOTS will have to pay...all of them, not just the participants in the job action.
The moral of the sory is that the feds have labor by the short hairs with the RLA. ALPA should be vigorously campaigning to roll back the RLA.