The Union Label
It's worth remembering that union rank and file aren't the same as union leadership. The former are generally just hard workers trying to get by and raise families. They participate in some political stuff out of union loyalty for the most part. They vote Democratic mostly because their dad did, back when Democrats were people like Hubert Humphrey and John Kennedy. If you asked their opinions on day-to-day issues, you would probably think they were conservatives.
Union leadership, on the other hand, often has a definite left-wing political agenda. They are found more often hanging out in Washington DC than they are in the industry towns.