"Which Side Are You On?" is a song written by Florence Reece in 1931. She was the wife of a union organizer for the United Mine Workers in Harlan County, Kentucky. In 1931 the miners of that region were locked in a bitter and violent struggle with the mine owners. In an attempt to intimidate the Reece family, deputies hired by the mining company illegally entered and searched the Reece family home. Sam Reece had been warned in advance and escaped, but Florence and their children were terrorized in his place. That night, after the men had gone, Florence wrote the lyrics to "Which Side Are You On?" on a calendar that hung in the kitchen of her home. She took the melody from a traditional Baptist hymn, "Lay the Lily Low", or the traditional ballad "Jack Munro". Florence recorded the song and it can be heard on the CD Coal Mining Women.
Reece supported a second wave of miner strikes circa 1973, as recounted in the documentary Harlan County USA. She and others perform "Which Side Are You On?" a number of times throughout.