ABSTRACT This paper investigates the impact of regulatory changes concerning non-audit services (NAS) on corporate tax planning practices, focusing specifically on auditor-provided tax services (APTS). In particular, the study examines the implications of the European Union (EU) Audit Reform introduced in 2014 through Regulation No. 537/2014 and Directive 2014/56/EU, which imposed significant restrictions on the ability ofaudit firms to offer NAS, such as tax advisory services, to their audit clients. These measures aimed to enhance the reliability offinancial reporting and safeguard auditor independence, in light ofgrowing concerns about potential conflicts of interest arising from the joint provision of audit and non-audit services. To assess the effectiveness of this regulatory intervention, the study employs a Difference-in-Differences (DiD) empirical design using a panel of listed companies headquartered in five major EU economies (Italy, France, Germany, Spain, and the United Kingdom). The findings reveal that prior to the reform, there was no significant association between the fees paid for APTS and firms’ cash effective tax rates (ETRs), suggesting a limited role of APTS in tax planning outcomes. However, in the post-reform period, the study observes a positive association between APTS and ETRs, indicating that restrictions on APTS may have weakened firms’ ability to engage in effective tax planning. Notably, this effect is more pronounced in countries that chose to reinforce the EU-mandated limitations, suggesting that national discretion in implementation plays a relevant role in shaping regulatory outcomes. This study contributes to the existing literature by expanding empirical knowledge on the relationship between APTS and corporate tax planning in a European context, an area that remains underexplored compared to U.S.-focused studies. It also offers the first evidence on how the EU Audit Reform may have unintentionally influenced tax planning effectiveness, thus responding to recent calls for more research on the broader economic implications of audit regulation. Beyond its academic relevance, the study provides practical insights for regulators and policymakers. It highlights the trade-offs between enhancing auditor independence and preserving the informational synergies that may benefit clients’ fiscal strategies. Finally, it raises important questions about how regulatory design, particularly the degree offlexibility left to national governments, can affect both the professional judgment of auditors and firms’ tax behavior.
KEYWORDS: tax planning, auditor-provided tax services, European audit reform
