Political identity has become a critical social identity in the era of digital platforms. We study the impact of political identity disclosure on subsequent participation and polarization. Our context of study is a subreddit r/Tuesday on Reddit, which incorporated a policy that mandates users to declare their political ideological stance. Our results suggest that, after disclosure, there is a significant drop in participation on posts by new users, measured by the number of new user comments that a post receives. In addition, we also observe a higher amount of polarization, measured by rule violations, the usage of slang and partisanship terms. Interestingly, users holding different political perspectives are affected disproportionately due to the mandatory disclosure policy. The most significant decrease in engagement has been found on users with unclear political stances. In contrast, the left-leaning users, the minority group, maintained a comparable amount of activity as before but used more slang and partisanship terms in their subsequent discourse.