I had a boss who was an expensive consultant for unions. He explained the reason unions in the US were shrinking is that they are too powerful. They control huge pension and healthcare portfolios and can completely control the relationship with employers, especially in closed shop situations. Comparatively, European unions are much "weaker" - or maybe more accurately their purview is much smaller. They control smalle…
I'm not sure I'd call unions legally-mandated to hold 33-50% (depending on company size) of the company's board seats "weaker". That's the situation in Germany.