Are you f'ing kidding me? Of course its an illegal job action. Of course the union HAS To put that out to protection. If anyone believes their tripe about no illegal job action ever advancing the pilots cause, they need to look at aviation history.
If anyone feels unethical about this or any other sickout, just read "Confessions of a Union Buster". Pilots by nature are not corrupt and want to get the job done, corporate management takes advantage of that in every way possible.