This study examines the value relevance of ESG disclosure across voluntary and mandatory reporting regimes. Specifically, we focus on the moderating role of environmentally sensitive industries. Using a sample of Thai listed firms from the voluntary period (2015-2020) to the mandatory period (2021-2023), we exploit the regulatory transition to examine the decision usefulness of ESG information. The results indicate that: (1) ESG disclosures are positively associated with stock price in both regimes, but there is no statistically significant difference; (2) the value relevance of ESG disclosure is significantly weaker for firms in environmentally sensitive industries (ESI) compared to their non-ESI peers; (3) industry sensitivity negatively moderates the value relevance of ESG disclosure under the voluntary regime, but the negative moderating effect disappears following the transition to the mandatory regime. Our findings suggest that, under the voluntary regime, disclosures by ESI firms highlight regulatory risks and proprietary cost concerns, leading to a valuation penalty. However, mandatory disclosure levels the playing field by standardizing reporting, enabling ESI firms to provide transparent disclosures without being penalized by the market.