I think the reason unions tend to be industry-specific is because the execs for a certain industry tend either to collude or snipe at eachother depending on the situation. So if an entire industry goes on strike it means that one company can’t capitalize on the opportunity of another company going on strike. In theory, if the widget-maker’s union goes on strike, it means the entire supply chain of things made with widgets gets choked, which exerts a lot of financial pressure on management.