The Communist Party of Canada is a federal political party in Canada. Founded in 1921 under conditions of illegality, it is the second oldest active political party in Canada, after the Liberal Party of Canada. Although it does not currently have any parliamentary representation, the party's candidates have previously been elected to the House of Commons, the Ontario legislature, the Manitoba legislature, and various municipal governments across the country.

The One Big Union (OBU) was a militant left-wing industrial union based primarily in Western Canada. Launched formally in Calgary on June 4, 1919, the OBU, after a spectacular initial upsurge, lost most of its members within a few years. It eventually merged with the Canadian Labour Congress in 1956.