Carbon transparency, once a niche practice, is increasingly becoming institutionalized. Firms are now required to report not only their operations' carbon emissions but also their suppliers'. This research explores the institutional pressures emanating from buyers and industry peers driving supplier firms to disclose high‐quality carbon emission publicly—our concept of carbon transparency. Many firms are increasingly adopting incentives to engage their employees in corporate climate change programs. Thus, we study the impact of three institutional pressures—coercive, mimetic, and normative—and examine when these pressures are more (or less) effective for driving supplier carbon transparency depending on the presence of climate change incentives. We used Carbon Disclosure Project's supply chain program (CDP‐SCP) as our research context. To gain deeper insight into the CDP‐SCP as well as the drivers and challenges of suppliers' carbon transparency, we conducted interviews with three CDP officials, three CDP‐SCP members (i.e., buyers), and six CDP‐SCP participants (i.e., suppliers). To test our hypotheses, we used a unique dataset from CDP‐SCP and complemented it with four other archival datasets for a sample of 835 suppliers operating in 41 countries during the 2013–2015 period. The results show that suppliers without climate change incentives are more vulnerable to coercive and mimetic pressures, whereas suppliers with climate change incentives are more receptive to normative pressure in terms of how much carbon transparency they exhibit. Thus, our study proposes an extensive concept of supplier carbon transparency, provides a comprehensive analysis of its external/internal drivers, and reveals when institutional pressures are more/less effective in eliciting supplier carbon transparency. This research also provides strategies for how buyers, suppliers, and CDP can foster more carbon transparency in supply chains.