Purpose: This study aims to examine the impact of different levels of required book-tax conformity (BTC) on audit clients' demand for auditor-provided tax services (APTS). In addition, the authors also investigate the effects of the European Union (EU) Regulation (2014). Design/methodology/approach: This study utilizes a sample of listed companies from 10 EU countries between 2010 and 2019. The final sample consists of 16,049 firm-year observations from 2,515 unique firms, and the authors use both probit and ordinary least square (OLS) regression models in this study. Findings: The main finding of this paper is that companies listed in countries with a higher level of BTC are less likely to purchase tax services from incumbent auditors and pay fewer auditor-provided tax service fees. Results from further analyses confirm that firms substantially reduced their purchase of APTS after the EU Regulation (2014) was implemented, but these reduced purchases were found to be more pronounced for firms located in countries with low BTC. Originality/value: This study advances the understanding of the determinants of APTS and the consequences of BTC. Specifically, the authors report that variation in a country-specific feature (i.e. BTC) also affects firms' decision to purchase APTS. Moreover, this paper provides some preliminary evidence of the new regulation and contributes to the literature on APTS regulation. The findings of this study have important policy implications for regulators and are also relevant for various capital market participants.