For a number of Western democracies, it has been observed that the preferences of poor and rich citizens are unequally represented in political institutions and outcomes. Yet, the causes of this phenomenon are still under debate. We focus on the role of elections in this process, by disentangling biases towards different income groups that stem from the party system and from voters' behaviour. Our aim is to uncover whether elections as selection mechanisms contribute to unequal representation by analysing factors of the supply and demand sides of the electoral process. On the supply side, we focus on the congruence of parties' policy offers and voters' preference distributions. This shapes citizens' possibilities to express their policy preferences. On the demand side, we are interested in the extent to which citizens from different income groups base their vote decisions on their policy preferences. The empirical analysis relies on the European Social Survey and the Chapel Hill Expert Survey and covers 13 Western European countries. Our results indicate, first, that the economic and cultural preferences of poor and rich citizens differ significantly, and second, that party systems in the countries under investigation represent the lowest income groups the worst, and the middle income groups the best. This makes it difficult for citizens at both the lower and the higher end of the income distribution to voice their preferences in elections. Additionally, we show that low income citizens tend to take policy less into consideration when making an electoral choice than richer citizens. Thus, while the rich make up for their representation bias by taking policy more into account in their voting behaviour, the electoral stage poses another obstacle for the poor to overcome the representation bias. In summary it can be said that already on the supply side there is an unbalanced disadvantage in terms of representation for the very poor and the very rich, but the pattern leads to an even more asymmetrical misrepresentation of the poor due to the election act.