Ah, this is very different from how unions work in France (and, generally speaking, in the EU).

Some people are actually registered with an union but their challenge is to have people vote for them during compulsory elections for work councils.

Any employee can vite, and any employee can join a union. The mere fact of joining the union does not protect you form being fired (which by itself is very complicated in Europe where there are strong labour laws). The only people who are strongly protected are the ones who create a union, or are elected as a representative.