We conduct a natural field experiment with a major European party to test whether giving party supporters the opportunity to voice their opinions increases their subsequentengagement in the party’s campaign. In our experiment a random subset of party sup-porters are asked for their opinions on the importance of different topics either (i) in thecontext of improving electoral success of the campaign, or (ii) for them personally. We show that giving supporters more opportunities to voice their opinions increases their engagement in the campaign as measured using behavioral data from the party’s smartphone application. Survey data reveals that our voice treatments also increase other margins of campaign effort as well as perceived voice. The effects on campaign effort and perceived voice are driven by respondents asked to give their opinions in the context of improving the electoral campaign. Our evidence highlights that parties can increase their members’ investment in the democratic process by implementing policies that increase their voice.