I will just mention that my maternal grandfather was a founding member of the CIO in the state of Ohio, being a machinist. Before that, his father had been a member of the IWW (Go, Wobblies!). My grandfather rose through the union ranks to become head of the political arm of the CIO in the state, and held the post even after the AFL and CIO merged in the 1950's.
My paternal grandfather kept his position with the Lehigh Valley Railroad during the Great Depression because, even though by the 1920's he had moved to a low-level front office job, he kept his union dues paid up. He went back on the road and stayed there until his retirement.
My father was a member in good standing of both the NEA and the NYEA, and was a negotiator with the Waverly, NY Central School District during the 1970's.
All I will say, in the words of the old ILGWU song, is look for the union label.