If you were Chinese or Indian, unions were directly responsible for your deportation. If you were Japanese, unions were directly responsible for your family's forced internment. If you were Puerto Rican, unions were responsible for the genocide that was committed against your mother, wife, and daughter. The AFL wan't shy in the least about its intentions. If you read the contemporary writings of its leaders, as well as the mass media that they produced (flyers, pamphlets, etc.), they were very blatant about their desire to protect jobs for white members by stripping naturalized Americans of Asian descent of their citizenship and deporting them. The language that was used to describe Chinese workers mirrors the exact same dehumanizing comparisons to animals that were later used by the Nazis[0].
If you dislike the current US visa system, with its draconian system of per-country quotas, you have labor unions from the 1950s to thank for that as well.
It's highly unpopular to talk about this, and so I fully expect to take a hit for bringing this up, but it needs to be said.
[0] They even published a pamphlet which referred to the Chinese as a "race question" (https://en.wikipedia.org/wiki/Jewish_question)