How does transparency affect voting behavior? To answer this question we exploit a switch from a show of hands to electronic voting in the Upper House of the Swiss Parliament. The change, which took place halfway through the 2011–2015 legislative period, also brought about the online publication of individual voting records. Using the Lower House as a control group, we compare individual voting decisions in a set of identical votes in both chambers. This unique framework makes it possible to estimate the causal effect of increased transparency on legislators’ choices. Since the reform, members of the Upper House are less likely to deviate from the majority decision of their party. Legislators representing the same canton are also less likely to cast an aligned vote, suggesting that voters lose influence over their representatives in parliament.