This article applies securitization theory to account for the proscription of organizations linked to Euskadi Ta Askatasuna (ETA) in Spain. I argue that securitization is vital for understanding the evolution of Spanish counterterrorism policy from tolerating to banning political organisations not directly involved in terrorist attacks, but supporting and sympathetic to ETA. More specifically, I examine the role of the judiciary in the initiation of securitization processes in which ETA came to be conceived as a “complex structure” integrating armed and unarmed activists, and the resonance of judicial securitization frames in the public sphere. I do so by analysing evolving conceptions of the relationship between ETA and two organizations—the youth group Jarrai and its successors Haika and Segi and the ETA prisoners’ lobby Gestoras proAmnistía and its successor Alkatasuna—as articulated in court rulings and a sample of 573 newspaper articles published in the Spanish daily El País between 1994 and 2016. I argue that two modes of securitization can be observed in these cases, one extending security threats posed by ETA’s terrorist strategy to the political organizations and one framing both the terrorist group and political organizations as threats to the democratic community.