With the growing interest in sustainability, brands increasingly use social media not simply to advertise their products but also to share their positions on ongoing public issues. This study investigates the effect of public-issue posts on consumers’ active reactions and provides comparisons between two samples—public-issue posts and all Twitter posts. After collecting data from Twitter based on tweets from official sportswear brand pages, we find that public-issue posts have a positive influence on consumers’ active reaction (i.e., number of retweets, number of quotes, number of replies, and post-social search behavior). Moreover, the effect of brand activeness, which is brand social activity on Twitter, and media type (photo or video presence in a tweet) are included in the analysis. With user engagement in the public-issue post sample, the effect of the media type is not significant, whereas the effect of brand activeness is significant. This study aggregates literature on brand activism and environmental, social, and governance (ESG) criteria to propose a measurement for a public issue in a single post rather than at the corporate level. The results of this study are useful for brands of all scales taking sustainable marketing strategies and aiming to improve interactions with consumers on Twitter.