Bluebird Mine workers were the last holdouts to join a union in Butte, Montana. Butte was the origin of much of Montana’s early labor movement. It was known as the “Gibraltar of Unionism.” On June 13, the Bluebird workers shut down mining operations and marched to the union hall to be initiated into the Butte Miners’ Union. This created a “closed shop” in Butte’s mines that lasted 27 years.