We examine the effect of campaign financial disclosures on support for Washington State Initiative 1634, a ballot initiative aimed at limiting tax increases on soda. In an experimental setting, we assess the effect of financial disclosures when paired with the actual textual arguments provided to Washington State voters and the effect of financial disclosures when paired with more complementary textual arguments. We find evidence that financial disclosures influence changes in voter support for the tax initiative. Specifically, our findings indicate that disclosing the top financial contributors “for” and “against” the initiative provides decision-relevant information to voters. Thus, policymakers should consider (1) making donor disclosures freely available in voter information guides, (2) eliminating special-interest group techniques that hide the sources of contributions, and (3) erring on the side of caution when constituents seek to remove ballot-related financial reporting requirements.