Pricing sustainability assurance under the CSRD: how fee structures reflect market power and institutional fragmentation

Purpose This study aims to examine how sustainability assurance (SA) fee structures under the Corporate Sustainability Reporting Directive (CSRD) reflect market power, regulatory differentiation and institutional fragmentation. While prior research documents auditor concentration and widespread bundling of SA with financial audits, little is known about the pricing mechanisms through which professional dominance emerges during the early implementation of mandatory SA. Design/methodology/approach The authors analyse hand-collected audit and SA fee data from 263 Euro Stoxx 600 companies reporting for the 2024 financial year, the first year of CSRD application. Of these firms, 93 provide separate disclosure of SA fees, enabling descriptive analysis of fee magnitudes, ratios, sectoral concentration and cross-country disclosure practices. Findings Three patterns emerge. First, fee disclosure is institutionally fragmented: 73.8% of French firms disclose separate SA fees, compared with only 13.0% of German firms, reflecting national corporate law differences that systematically constrain transparency. Second, financial institutions account for a disproportionate share of absolute SA spending, paying mean fees of €2.63m versus €0.69m for non-financial firms, consistent with sector-specific regulatory demands interacting with CSRD requirements. Third, SA pricing is regressive: smaller firms incur SA fees equivalent to 30–43% of audit fees, while large firms pay 1–5%, alongside near-universal bundling and strong provider concentration. Practical implications Findings suggest mandatory granular fee disclosure standardisation at EU level, scrutiny of how prudential frameworks create sector-specific demand benefiting incumbents and interventions addressing regressive pricing. Recognition that Omnibus scope reduction may intensify concentration among remaining large-cap filers makes market-structure interventions more urgent. Originality/value The study provides the first large-sample evidence on CSRD SA fees and suggests how pricing structures reinforce professional dominance through transparency fragmentation, regulatory stratification and regressive pricing. By documenting baseline outcomes prior to the CSRD scope reduction, the paper contributes to important accounting debates on accountability, regulation and the political economy of mandatory SA.