While there has been a sufficient amount of research and empirical evidence on the factors that influence a company’s decisions to voluntarily disclose carbon information, little research has been done on the carbon disclosure practices of ETS-affected companies, in Asian countries, in particular. Considering this, it is essential to shed light on more diverse linkages between carbon performance and voluntary carbon disclosure (VCD) under ETSs taking into account the specific context of each individual country. Drawing on the Korean ETS-affected companies with a contents analysis of their sustainable reports from 2015 to 2019, the present research seeks to address the existing knowledge gaps in the current literature on carbon disclosure. In doing so, hierarchical ordinary least square (OLS) regression analysis is used to infer causality and assess the findings. The findings empirically prove a positive relationship between carbon performance and VCD, which means that the affected companies under the Korean ETS are likely to disclose more when they have favorable carbon reduction performance. Furthermore, this link tends to be amplified for companies with a high percentage of foreign sales, while the role of media visibility interacts differently with carbon performance in influencing VCD.