This paper studies the motives behind socially pressuring others in the context of voter mobilization. In this online experiment, college students choose whether to send an email that pressures their campus peers to register to vote for the 2020 U.S. Elections. The senders have a negative average willingness-to-pay (WTP) to send the email, meaning they would rather pay than pressure their peers. The experiment reveals two counteracting motives at play. On the positive side, senders believe that pressuring their peers will persuade them to register. On the negative side, they believe that their peers will dislike being pressured, which outweighs the positive motives. However, under anonymous messaging, they become much less sensitive to whether the recipient dislikes being pressured, and their average WTP turns positive. This pattern of behavior reflects voters who are motivated by the prospect of mobilizing their peers, but are restrained by self-interested concerns from social costs or retaliation.