Labels can be deceiving, the devil is in the details. Unions in this country were not always on the progressive side, in fact they often provided coverup for US capital attacking labor overseas. Moreover, they were instrumental in the SUV "revolution" because it created jobs. I also understand that they are pretty much against immigration and, say, opening the US borders for Mexican truckers.
I'm sure that unions elsewhere would also espouse similar reactionary positions from time to time. So if the Greens oppose some these reactionary measures it does not mean that the Greens should be automatically judged "enemies of the left." In fact, it is the organized labor that should.
The Green position can have high long term benefits for the working class (and everyone else) than the organized labor trying to get short term gains by going to bed with the capital.
Wojtek