The Internet has emerged as an important communication platform for the support of collective action, but little is known about how it influences the psychosocial motives for participation. Two quantitative studies were conducted within two different mobilizing contexts, in which offline collective actions were launched through computer-mediated communication. We examined whether and how the frequency with which people participated in online political discussions moderated the effects of the psychosocial predictors of collective action, specifically politicized identity, anger, collective efficacy, and morality. Results showed that collective action intention was predicted by politicized identity only when participants reported a higher versus lower frequency of online discussion. However, anger did not predict collective action when people had the chance to express this emotion through a higher versus lower frequency of online discussion. Moreover, collective efficacy and morality supported collective action intention in participants who reported a higher versus lower frequency of online discussion. We theorize on how computer-mediated communication, and its specific features, can be studied as a mobilizing context that influences the psychosocial motives to participate in collective action. Copyright © 2012 John Wiley & Sons, Ltd.