This ethnographic study examines the role of ideology in the development of organizational dilemmas in the Clamshell Alliance, an anti-nuclear protest group active in New England during the late 1970s. In 1977, the Alliance received national recognition for its use of consensus decision making and nonviolent civil disobedience during a highly publicized two-week incarceration following an attempted occupation of the Seabrook nuclear plant. But over the next few years, sharp internal disagreements developed over the use of these strategies, leading ultimately to a factional split. I extend theory from symbolic anthropology to integrate the analysis of ideology into the study of resource mobilization without sacrificing the latter's emphasis on rational calculation. My analysis shows that the Alliance's anti-nuclear ideology established an egalitarian identity for the group which structured both the initial selection of strategies and later efforts to modify them.