Most CIO organizing was based on a mass collective action, high-participation model anchored in deep worker solidarities and cooperative engagement in class struggle. Strikes, the kind that could shut down production—strikes in which most if not all workers walk off the job in a high-risk collective action—were routine, and were evidence that workers themselves were the primary agents of their own liberation. “Left” organizers, those associated with various socialist and radical factions, flocked to the CIO because of the principal of inclusion, of uniting all workers across ethnicity, gender, race, skill level, and every other working-class division. The AFL had had a long, complicated history not just of excluding semi- and unskilled workers, and Black workers, but also of having taken positions against European and then Asian immigration, and very narrowly limiting the union struggle to wages and working conditions.

The CIO’s left organizers were intensely committed to recruiting and building power across the many “isms” and other divisions among the working class, and they had to develop special methods to do it. Jack O’Dell, an organizer for the CIO and later for the civil rights movement, recalls their success: “I grew up in Detroit, and when people asked you, ‘What union are you in?’ the guys didn’t even say their union; they just said, ‘the CIO.’ Especially black workers, because the CIO would take on racism.”