EU Member States have implemented a new regime designed to discourage aggressive cross-border tax planning."DAC6" or the 6th Directive dated 25 June 2018 on the Administrative Cooperation between EU Member States requires intermediaries to disclose information regarding certain cross-border arrangements to their local tax authorities in order to create a system of fair taxation within the internal market. Most importantly, the intention is to arm the tax authorities with information about potentially aggressive arrangements as early as possible, enabling them to close down loopholes or challenge the tax treatment claimed by taxpayers. The UK had also implemented DAC6, but HMRC has meanwhile, as a consequence of Brexit, considerably limited its scope and announced the implementation of the OECD’s Mandatory Disclosure Rules (MDR).

DAC6 requires intermediaries (such as lawyers, consultants, financial institutions) – or in certain circumstances their clients themselves – to report any advice relating to and/or the implementation of a cross-border arrangement of potentially aggressive tax planning to the local tax authorities. Aggressive tax planning is evaluated on the basis of certain objective indicators called "hallmarks". For some of these hallmarks to be relevant, one of the main motives of the arrangement must be obtaining a tax advantage. Others will just be reportable on the basis of specific indications of which the intermediary is (supposed to be) aware.