Previous research shows that positive contact with members of advantaged groups can undermine collective action among the disadvantaged. The present work provides the first experimental evidence of this effect and introduces a moderator which highlights the fundamental role of communication about perceptions of the legitimacy of intergroup inequality. Study 1 (N = 267) focused on the lesbian/gay/bisexual/transgendered community's struggle for same-sex marriage in California. In Study 2 (N = 81), cross-group contact was initiated between members of two universities that differ in social status. Results revealed that positive cross-group contact undermined public collective action among the disadvantaged when the advantaged-group partner described their group's advantaged position as legitimate or when they did not communicate their feelings about intergroup inequality (leaving them ambiguous). In contrast, when the advantaged-group partner clearly described the intergroup inequality as illegitimate, cross-group contact did not undermine participation in public collective action.