Emphasizing a distinction between interpersonal versus intergroup behavior, this paper investigates the impact of interpersonal and intergroup characteristics on the individual's decision to rely on collective action. Four dimensions of interpersonal versus intergroup behavior--social mobility versus social change, personal deprivation versus group deprivation, self-identity versus group identity, and variety versus uniformity of opinions--are presented as integral parts of the social psychological processes of categorization, identity, and comparison that underlie the individual's decision. Applied to survey data from 83 school districts in New York State, measures of these dimensions and of perceived legitimacy of power in the district are used to predict elementary and secondary teachers' desire to have the union become involved in compensation issues and issues of professional prerogative. Results of regression analyses show the importance of both interpersonal and intergroup factors, particularly deprivation and identity, in deciding to rely on group action. Differences in results between elementary and secondary school teachers, as well as between compensation issues and issues of professional prerogative, reinforce the validity of making these distinctions. Suggestions are made for the further development of the social psychology of interpersonal versus intergroup behavior. (Author/MJL)