"Matewan" is pretty good, directed by John Sales and Hazel Dickens appears in it, singing. But Matewan is a fictional piece.
"Harlan County, USA" is a very good documentary about miners trying to get a company to accept a union contract, shot back in the early 1970's. The filmmaker, Barbara Kopple, was probably an out-and-out communist -- but the finished work is worth watching, nonetheless.