This paper seeks to develop and test an issue-level determinants model of opinion congruence inequality between the privileged and the underprivileged social groups. Current theories on congruence inequality and representation focus on country-level factors such as the interest group system or campaign finance. The existing literature focuses far less on variation in inequality in preference representation in a single context. To fill this void in the literature, we develop an issue-level model of opinion congruence inequality between the privileged and the underprivileged groups in terms of education and income. Based on an integrated dataset containing the policy positions of parties and voters in Belgium on 229 policy statements, we find that when social groups have different policy positions, preferences in the legislature align more with the preferences of the privileged social groups. In addition, opinion congruence inequality also depends on the importance of the issues to groups: the difference in opinion congruence is larger for economic and tax policies, vital to the privileged groups, but smaller on issues related to social welfare, crucial to the underprivileged groups. Finally, the results show that when voters of a group disagree with their party’s position on an issue, their preferences regarding that issue are less well represented in the legislature.