When is mobilization of group identity successful? Work on social movements suggests that frames that target group identity can mobilize groups. However, this work does not address when group mobilization using frames is likely to be successful. Recent work on source credibility finds that same-group sources are an important moderator of framing effects, and previous work on stakes of the decision shows that individuals in high stakes are more likely to participate than those in low stakes. I combine these two moderators of frames to generate predictions for when group sources are most likely to be credible. I test these predictions in the context of a public goods game laboratory experiment in which targeted frames are given to group members by sources that share their group identity and in which stakes of the decision are varied. The findings of this project have implications for political mobilization and campaigning based on group identities.