There is increasing pressure on political organizations such as the European Commission to provide openness about how special interests influence policies. In response, lobby registers are set up to provide information about the topic, date, and participants of meetings with policymakers. Interest groups use these registers to learn what competing groups are doing and may respond strategically. To evaluate the strategic changes due to increased transparency, I study a formal model where competing interests engage in informational lobbying over time. The focus is on how observing lobbying behavior of competing groups---transparency---affects the amount and timing of information provision. I show that transparency may be disadvantageous because groups are dissuaded from acquiring information if they learn that competitors have disclosed favorable information for their cause. Conversely, transparency allows interest groups to be selective in acquiring information and may lead to more informed decision-making. Further, a transparent institution causes changes in the timing of disclosure because interest groups trade off potentially scaring off competitors with early disclosure and waiting to learn whether further information acquisition is necessary.