Barbara Kopple's 1976 chronicle of a Kentucky coal-mining strike. Won Best Documentary at the Oscars; remains the high-water mark of US labour documentary.
From Wikipedia
Harlan County USA is a 1976 American documentary film covering the "Brookside Strike", a 1973 effort of 180 coal miners and their wives against the Duke Power Company-owned Eastover Coal Company's Brookside Mine and Prep Plant in Harlan County, southeast Kentucky. It won the Academy Award for Best Documentary at the 49th Academy Awards.