Copyright © 2020 (Özden Melis Uluğ, Özen Odağ, and Nevin Solak).This contribution examines a case of collective action in Turkey against a sexist advertisement. Protests unfolded exclusively through social media and resulted in more than 20,000 protestors signing a petition against the ad. In this study, we examine protest motivations behind the case and study the degree with which these motivations are explained by (1) online/offline action practices, and (2) three social-psychological variables (social identity, perceived efficacy, and just-world beliefs). Survey data from 353 participants were analyzed by means of hierarchical linear regression. Results indicated that protestors were mobilized by their identification with women's rights defenders, their perceptions of collective efficacy and both offline and online action practices. In addition, just-world beliefs were negatively associated with collective action. Our findings confirm and expand recent findings of the relevance of social-psychological predictors for collective action in the online sphere. At the same time, the case points to the facilitating power of social media toward change in Turkey's current authoritarian climate.