Abstract
We consider collective decision problems where some agents have private information about alternatives and others don't. Voting takes place under strategy-proof rules. Prior to voting, informed agents may or may not disclose their private information, thus eventually influencing the preferences of those initially uninformed. We provide general conditions on the voting rules guaranteeing that informed agents will always be induced to disclose what they know. In particular, we apply our general result to environments where agents' preferences are restricted to be single-peaked, and characterize the strategy-proof rules that ensure information disclosure in this setting.