This article describes US unions’ efforts at capital stewardship, that is, the investment and management of the assets accumulated in pension and other retirement plans (frequently termed ‘workers’ or ‘labour’s capital’) — on behalf of plan participants and in the interest of workers more generally. It focuses particularly on the opportunities for direct worker voice in the governance and management of those assets through workers serving as trustees of the plans. The article explores the challenges these trustees face in navigating that role in addition to their possibly conflicting role as a union member or official. It details unions’ visions for capital stewardship and their efforts to integrate trustees’ activities within the broader range of union activities. Finally, it describes ways in which unions have collaborated in support of their trustees and to develop a cross-union capital stewardship agenda.