If in the CRL base the pilots decide on a strike, approved by an official trade union (like REPA should be/become), FR can not fire anyone. FR must abide Belgian law. It is very simple really. One starts his/hers work in Belgium (crewroom) and not on a FR EI-registered aircraft so irish law is void.
A total block is the only solution to get better conditions in FR I'm afraid. It is very unfortunate for the passengers, but management only hears when the wallet is hurting.