In 1977, supporters of the Revolutionary Marxist Group and a separate Quebec organization, the Groupe Marxiste Revolutionnaire, united with the League for Socialist Action and the Ligue Socialiste Ouvrière to form the Revolutionary Workers League/Ligue Ouvrière Révolutionnaire which became the new Canadian section of the USFI. Socialist Challenge was the publication of League for Socialist Action.
See International Marxist Group for information about its weekly newspaper Socialist Challenge.
Socialist Challenge was a Trotskyist group in English Canada formed by former members of the Revolutionary Workers League/Ligue Ouvrière Révolutionnaire who were expelled or resigned when the RWL moved away from Trotskyism in the early 1980s. The ex-RWL members formed a number of groups under various names in cities across Canada such as the "Socialist Workers Committee" in Toronto. They regrouped as the "Alliance for Socialist Action" and, in 1988 adopted the name Socialist Challenge (after the name of their newspaper) as a result of an organizational fusion with the Quebec group Gauche Socialiste (the formal name of the group was Socialist Challenge/Gauche Socialiste). Socialist Challenge was initially a sympathizing section of the United Secretariat of the Fourth International but became the USFI's official section in English Canada in the late 1980s after the RWL, now called the Communist League, left the USFI.
Socialist Challenge joined the New Socialist Group soon after the NSG's founding in 1996. Socialist Challenge became a tendency within the NSG and the newspaper Socialist Challenge ceased publication in favour of the NSG's New Socialist. In 1999, Socialist Challenge formally dissolved as an independent group and became the Fourth International Caucus of the NSG. The caucus remains the official English Canadian section of the USFI.
Gauche Socialiste still exists as an autonomous section of the Fourth International, and has "fraternal relations" with the NSG.