Previous research has shown that consumers increasingly challenge the legitimacy of marketers and unsolicited marketing communication in online contexts. Based on a qualitative study, this article examines how and for what reasons consumers challenge marketer legitimacy—the perceived appropriateness of marketers and their activities—in the empirical context of Reddit, a popular social news and community website. The study suggests that consumers challenge or accept marketer legitimacy in online communities based on particular, community and situation specific, legitimacy criteria that reflect and reproduce the values and norms of the community. In doing so, it is argued, consumers play a role as legitimating agents—consumer‐citizens that have the power to confer or deny legitimacy in the context of business‐society relations. Overall, the study advances knowledge in the field of consumer studies in two ways. Firstly, it builds a symbolic interactionist perspective on consumer‐citizens as legitimating agents who enact their active citizenship role in the marketplace by assessing and constructing marketer legitimacy in online communities. Secondly, it offers an empirically grounded account of how and for what reasons consumer‐citizens challenge or accept the legitimacy of marketers and unsolicited marketing communication in online communities. This article is protected by copyright. All rights reserved.