Countries that use proportional representation (PR) tend to have higher levels of redistribution. At the same time, countries do not choose their electoral systems at random, which means that PR countries are likely to have different background conditions than non-PR countries. We therefore ask if the strong empirical relationship between the use of PR and higher redistribution is due to these background factors or to PR electoral rules. We take advantage of an electoral reform to early 20th century Norwegian local elections to gain traction on this question. We find that municipalities that were mandated to use PR increased tax rates and resources spent on the poor but also redistributed less in the first place. We further show that the reform did not increase left-wing party seat shares but did increase political mobilization. This evidence is consistent with moderate parties increasing redistribution in order to preempt left-wing party gains.