Studies of inter-corporate influence have focused on structural, rather than relational, modes of organizational interaction. That is, inter-corporate influence is assumed to be a function of relationships between firms’ industries rather than of dyadic relationships between the firms themselves. Our study critiques and expands on one such stream of research (Mizruchi 1992; Mizruchi
& Marquis 2006) by focusing on relational predictors of influence in a study of similarity of corporate political action among large U.S. firms. We show that relational size is a key determinant of behavioral similarity, and that this mechanism varies across industry relationships. Implications of these findings, as well as the general importance of relational versus structural theories of influence, are discussed