Scientists increasingly engage in policy advocacy, especially on climate change. Does this advocacy undermine—or bolster—public trust in scientists and support for scientists' recommendations? We leveraged a unique opportunity to answer this question in a real-world setting: the 2023 referendum for the Swiss climate protection law (CPL), which was supported by a public statement of 252 renowned scientists across disciplines. We conducted a pre-registered, two-wave, quasi-field experiment (n pre-vote = 1,622, n post-vote = 891) to test how scientists' collective support for the law affected public trust in scientists and voting behavior. We found that scientists' advocacy was associated with greater public trust, particularly among left-leaning individuals; only a minority viewed these scientists as not objective. However, perceptions of scientists' role in society and policymaking and voting behavior remained largely unaffected when participants were reminded of the CPL advocacy. Although we studied a restrained form of policy advocacy in a somewhat unique setting, our study challenges the widespread assumption that policy advocacy undermines public trust in scientists.