I don't think this will count, because it's mostly about how badly eccentrics without privilege are treated in society (and, tangentially, about the mind-numbing boredom of tending a sausage machine), but you might have a listen to Leon Rosselson's "Barney's Epic Homer" anyway, because it's a great song.

The lyrics are about halfway down this thread.

And Amazon has the song for download, with a brief sample, here.

I'll think more ... surely there are many actual labor songs about meat packing conditions.