This article explores the challenges of building international labor solidarity by comparing two campaigns that developed inside the Canadian labor movement. I critically compare and assess the campaign against South African apartheid in the 1980s and the more recent efforts to oppose Israeli apartheid. Both campaigns are examples of grassroots international labor solidarity, where organizers sought to build international solidarity through member mobilization and a focus on the power of workers to engage in solidarity actions. I examine how these union activists organized within their unions, and how their organizational differences and the ideological and political contexts they organized within shaped their successes and limitations. Drawing from the work of Antonio Gramsci, I argue that these campaigns were sites of counter-hegemonic practice both because of the analysis and critiques they offered but also because of the nature of their organizing.