There's many different unions as far as cunstructuon workers go, I'm surprised this is a new thing for you. Plumbers, electricians, iron workers, general labour, hvac, elevators, drywallers, and I'm probably missing some, all have unions.
Just to clarify, I have heard of variety of unions, I just don't recall hearing plumbers or electricians for example being on a strike.
If everyone was like you or your union perhaps there would not be such a negative view of them ... but that's hardly the case. The way some of them consider seniority, banking sick days, sick leaves ..... is just mind boggling in today's environment and especially compared to people who work in private non-unionized sector.