The aim of this article is to compare and contrast three different approaches towards non-audit services (henceforth “NAS”) based on: 1) researchers’ views, 2) the EU regulation, and 3) the provision of NAS by the Big-4 firms operating in twenty-seven EU member states. Therefore, the article includes: (i) a literature review of various NAS aspects, (ii) an analysis of the EU reform in terms of NAS, and (iii) an empirical analysis of NAS fees which have been disclosed in the Big-4 transparency reports for the period 2017-2019.The literature review shows: a) lack of consensus between researchers about the potential consequences of the NAS provision in general, b) quite limited or little evidence of the consequences of the NAS restrictions as part of the EU audit reform, c) ambiguity in terms of the NAS definition itself which results mainly from insufficient NAS disclosures and lack of a detailed NAS split.The EU regulators addressed these concerns only in very narrow aspects, i.e., through: (1) the NAS black list, (2) the NAS cap, and (3) the strong emphasis on public-interest entities (henceforth “PIEs”). What is more, NAS disclosure requirements in the transparency reports are limited only to two categories.Finally, the results of the empirical study indicate the significant differences at the NAS fee level among the EU member states. The analysis shows a particular importance of NAS fees from other clients as a substantial revenue stream for the Big-4 firms. The results suggest also a significant increase in this category in 2018 when NAS fees from other clients increased by net EUR809 million (13%). However, this strong trend was not confirmed in the following year.All in all, the study underlines deficiency in proper NAS disclosure and reporting which might be observed also in the case of transparency reports. All findings of this study may be another argument for regulators to address the problem of NAS in more detail starting from their advice on a NAS taxonomy which might be used then as a point of reference. It would be also beneficial for researchers exploring the NAS aspect and, thus, may enhance data and results comparability between studies. Additional disclosure requirements like NAS provided to PIEs or a recurring or non-recurring character of NAS would also support the better understanding and evaluation of the consequences of the EU audit reform.