The Reesor Siding strike of 1963 was one of the defining labour conflicts in Canadian history, resulting in the shooting of 11 union members, three of whom were killed. The violent confrontation occurred near the small Francophone hamlet of Reesor Siding, which is located just west of Opasatika, approximately halfway between Kapuskasing and Hearst in Northern Ontario.

Opasatika is a township in the Canadian province of Ontario, located in the Cochrane District on the Opasatika River, a tributary of the Missinaibi River. Its name is of First Nation origin, meaning "river lined with poplars".