I can very easily believe that a Southern-based labor party in the 1870s would support white supremacy, although I'd also imagine that some unions will have to hold their noses to take part and that others will opt out altogether.
Okay, well, I think you and I are actually mostly in agreement re: Southern labor. And that things were indeed a little more complex than I let on(I did realize that segregation did occur in unions, btw, I just forgot to mention that).
BTW, I apologize if my last response seemed a tad muddled and clunky; I don't like to admit this but sometimes it's just hard for me to word things really well. Not to mention I was just plain tired.