Jews and communists were heavily represented among them, some of whom assembled in informal movements such as Main-d'oeuvre étrangère and Main-d'œuvre immigrée (as in neighbouring France).
When the war began, Solidarité juive was one of these associations and worked closely with the Comité de Défense des Juifs, and with Secours mutuel (left-wing Zionists).
Members of Solidarité juive were active in rescuing and hiding Jewish children, but also as armed partisans in the Front de l'Indépendance and as information agents in Leopold Trepper's Red Orchestra, based in Brussels.
[3] The objective of the UPJB is "The promotion of a contemporary, secular, and progressive Judaism in the diaspora, in the filiation of the struggle of the workers movement and of the anti-Nazi resistance.
"[5] In 2001, UPJB, through an open letter signed by its then president Elie Gross, supported the main Belgian French-speaking daily Le Soir during a campaign from the Belgian Zionist organizations, including the CCOJB, which accused its journalists of a systemic anti-Israeli bias.