Republic Steel was one of the last major steel firms to use low-phosphorus Adirondack magnetites, operating the Chateaugay Ore & Iron Company in Lyon Mountain, New York from 1939 to 1967. The Chateaugay mine was one of the deepest commercial iron ore mines in the United States, with stopes as much as 3,500 feet (1,050 m) below the surface.
On Memorial Day, hundreds of sympathizers gathered at Sam’s Place, headquarters of the SWOC. As the crowd marched across the prairie towards the Republic Steel mill, a line of Chicago policemen blocked their path. The foremost protestors argued their right to continue. The police, feeling threatened, fired on the crowd. As the crowd fled, police bullets killed ten people and injured 30. Nine people were permanently disabled and another 28 had serious head injuries from police clubbing.