In Eastern Canada our unions have become problematic too, though they're not as vile as France's.
My first experience were of course were teachers. At least half of them hates children but love being the boss in the room. Most of them quit before because obtaining their seniority, and they tend to be the more conscientious ones. In 6th grade I had a teacher fired because she physically assaulted me multiple times by hitting me on the arms, during most of the scholar year. Did I say fired? No sorry, only unpaid leave for one week, and she was replaced by none other than... her son, because seniority I guess. In primary school our physical education teachers were obese.
The whole region (multiple cities in a rural area) where I grew up saw auto dealerships workers on strike / lock out for years. It began at the end of high school, at the end of university it was still going on 5~6 years later.
My first ever was in a grocery store, I was fired because "finally the union wants that job".
Stories I've heard from others abound: solder a lose component on a PCB? That's tech's job. Caught talking to a union member alone? Let's just say if having half the people you meet giving you death stares not enough, then be ready to defend yourself against all paranoid claims made against you. Army sub-contractors caught stealing gas masks and laptops by MPs?? Nah, "you have to build a file before firing them". People who did the coop programs (5 paid internships) in unionized organizations came back with quite a few horror stories of their own.
The worse is that we're forced to join and pay (at least software is pretty much free from unions), so much for liberty of association. Most votes are held with show of hands. They can be done secretly, but the vote to do that is also a show at hand, good luck being "that guy" who defies the executives' wishes for a strike when the war chess is full. And that's not even mentioning the various corruption scandals involving intimidation, threats of violence and organized crime.