We use a change in the voting procedures of one of the two chambers of the Swiss parliament to explore how transparency affects the voting behavior of its members. Until 2013, the Upper House (Council of States) had voted by a show of hands. Legislators’ decisions could only be verified ex post through the time-consuming screening of online videos. In 2014, halfway through the legislative period, the chamber switched to electronic voting with online publication of individual decisions, significantly increasing transparency. Data cover individual voting behavior during the 20112015 legislative period. In a differencein-difference framework, the Lower House (National Council), serves as a control group. Not only have the voting procedures of the Lower House remained unchanged since 2007 but also the legislative texts of the votes we analyze are the same in both chambers. This unique framework makes it possible to estimate the causal effects of transparency on legislators’ choices. Members of the Upper House are significantly less likely to deviate from their party line after the reform. While parties benefit from improved conformity, voters lose influence over their legislators. Two legislators representing the same canton are less likely to cast an aligned vote if their parties have distinct party lines.