Organizational research has focussed almost exclusively on the role of legitimate categories of practices, strategies, and structures in organizational phenomena, while neglecting the creation and use of illegitimate categories. To address this gap, we draw on social theories of legitimacy and social semiotics to show how illegitimate cultural categorizations are dialectical, embedded within symbolic systems, and how they are used to shape organizational action. More specifically, we analyse the processes by which various participants construct categorical illegitimacy in ongoing public debate about a controversial energy source – oil from Alberta’s oil sands. These influential actors employ images and words to contest opponent organizations taking a discursive stake in this field as they struggle over the legitimacy of extracting this form of oil. Based on our study, we offer a model for understanding the visual and emotional processes of categorical legitimation and delegitimation