Two experiments tested the effects of organizational identification on individual decisions to cooperate. These decisions occurred in the context of a nested social dilemma in which individuals, subgroups, and the larger collective each held distinct and incompatible interests. In study one, when the two subgroups in the dilemma were from different real organizations, higher organizational identification caused lower cooperation with the collective (and higher cooperation with the subgroup) when the opposing organization had a purportedly individualistic culture and reputation. This interpretation was supported by the results of study two, which directly tested subgroup reputation as a moderating influence on organizational identification. Members of multiple departments within a single organization formed the subgroups in the dilemma. Organizational identification had a negative effect on collective cooperation, and a corresponding positive effect on subgroup cooperation, when decision makers perceived the opposing department to have an individualistic reputation.These studies identified conditions under which organizational identification negatively affected cooperation in collective endeavors both across and within an organizational boundary. I discuss the implications of these results for organizations that try to elicit cooperation by fostering members' organizational identification.