We do know that everyone who is a supporter of unions are usually hardcore democrat voters and especially those that work in public services, so that would explain a lot of them. I really think these polls are always weighted and skewed towards democrats and really never get a true sampling of what the people are really feeling and thinking.
So there’s that.
Rank and file private sector union members are mostly Republicans and strong MAGA Trump supporters.
Even that Commie FDR opposed public sector unions, but nowadays that’s what most of them are.