On October 1, 2017, Catalonia held a self-determination referendum despite strong opposition from state authorities. The central government deployed over 10,000 police officers and organized extensive and controversial operations to close polling stations, despite significant opposition from many citizens, the regional police, and Catalan firefighters. A few weeks later, on October 27, 2017, the Catalan Parliament proclaimed a Unilateral Declaration of Independence.This article focuses on the digital communication strategies in Twitter of the Spanish police forces (Policia Nacional, Guardia Civil) and Spanish Interior’s Ministry during the 2017 Catalan referendum crisis. More specifically, it aims to analyse this controversial "image work" intended to legitimize various degrees of police action within a highly disturbed public space and amid the blurring of collective identities in Catalonia. To this end, we will employ a semio-discursive approach in dialogue with Benedict Anderson's concept of the national imaginary. The goal is to understand the impact of the identity issue on the configuration of operations for justifying and denouncing public action according to Boltanski’s approach (1984). Through its linguistic component, these operations will be analysed as speech acts constituting "grammars" (Brigidou and Kaufmann, 2020) of justification and denunciation that contribute to the meaning of the events and referendum period.Thus, how did these forms of digital communication influence the interpretation of the events? What signs were shaped by these speech acts? Which regimes of belonging were emphasized? What role did national identities play in these grammars? These are some of the questions we aim to answer.