The instrumental power associated with voicing opinions to an authority was manipulated to observe the effects upon subsequent discretionary, extra-role behaviours. In two experiments, the provision of non-instrumental voice increased extra-role behaviours above a no voice condition. Experiment 2 also showed that this relationship was mediated by procedural-justice perceptions, but not respect from, or social identification with, the group. The implications of these data for current theory, as well as the possible moderating role of social identification, are discussed. Copyright © 2005 John Wiley & Sons, Ltd.