Through the lens of institutional theory and the theory of economic regulation, we assess the readability of European banks' annual reports by studying the introduction of the Single Supervisory Mechanism (SSM) as a quasi-natural experiment. Using AI resources, we developed a textual analysis. Then, we applied the Difference-in-Differences approach to compare banks supervised by the SSM – significant banks – with banks from European Union countries, only supervised by the National Supervisory Authorities (NSA) – non-significant banks. Over time, European banks have published more information in their annual reports. The SSM impacted the readability of significant banks' reports, which became shorter and presented plainer English than those of non-significant banks. Surprisingly, the reports of significant banks, whose NSA is a Financial Supervisory Authority, present higher readability after the SSM introduction than those whose NSA is the National Central Bank. This study contributes to the literature on the SSM and textual disclosure in the banking sector.