Environmental, Social, and Governance (ESG) concerns have gained centrality in the airline industry's strategic and regulatory landscape. While prior research has explored the effect of voluntary ESG disclosures on firm valuation, the market impact of regulatory ESG sanctions remains underexamined—particularly in sectors with high regulatory scrutiny like aviation. This study investigates stock market responses to 45 ESG-related enforcement actions issued by EU and UK regulators against 15 publicly listed airlines between 2000 and 2024. Using a standard event study methodology, we find significant negative abnormal returns, with cumulative losses exceeding -3.5 % in the [-5, +5] event window. Governance-related sanctions trigger the most severe investor responses, while social sanctions, though more frequent, have a more moderate impact. A clear temporal decay effect is also observed: the longer the delay between misconduct and public disclosure of the sanction, the smaller the market reaction—indicating information leakage and gradual price adjustment. This study adds new evidence on how ESG sanctions affect airline valuations, showing that compliance and transparency matter financially in a heavily regulated industry, like aviation.