Update 13 June 2019 for an interesting paper by Anil Yilmaz Vastardis and Rachel Chambers, comparing investment law and the relevant issues for corporate veil and human rights abuses, see here.
Update 21 September 2016. For an application in the environment field, see  EWCA Crim 1043 R v Powell and Westwood and analysis by Robert Biddlecombe, who brought the case to my attention.
Update 20 June 2016 the strict approach was confirmed in C-155/14P Evonik.
There is no general EU rule on the piercing of the corporate veil. Neither company law nor tort law is sufficiently (or in the case of tort law even embryonically) harmonised to be able to speak of much EU influence here. However in EU competition law, the principle is more or less established and may, one suspects, inspire in other areas, too. In Eni, the ECJ confirmed on 8 May the strong presumption of attribution in the case of shareholder control.
It is established case-law under EU competition law that the conduct of a subsidiary may be imputed, for the purposes of the application of Article 101 TFEU, to the parent company particularly where, although having separate legal personality, that subsidiary does not autonomously determine its conduct on the market but mostly applies the instructions given to it by the parent company, having regard in particular to the economic, organisational and legal links which unite those two legal entities. In such a situation, since the parent company and its subsidiary form part of a single economic unit and thus form a single undertaking for the purpose of Article 101 TFEU, the Court has repeatedly held that the Commission may address a decision imposing fines to the parent company without being required to establish its individual involvement in the infringement.
In the particular case in which a parent company holds all or almost all of the capital in a subsidiary which has committed an infringement of the European Union competition rules, there is a rebuttable presumption that that parent company exercises an actual decisive influence over its subsidiary. In such a situation, it is sufficient for the Commission to prove that all or almost all of the capital in the subsidiary is held by the parent company in order to take the view that that presumption is fulfilled.
In addition, in the specific case where a holding company holds 100% of the capital of an interposed company which, in turn, holds the entire capital of a subsidiary of its group which has committed an infringement of European Union competition law, there is also a rebuttable presumption that that holding company exercises a decisive influence over the conduct of the interposed company and also indirectly, via that company, over the conduct of that subsidiary.
In the present case, for the entire duration of the infringement in question, Eni held, directly or indirectly, at least 99.97% of the capital in the companies which were directly active within its group in the sectors in which there had been a violation of competition law. The ECJ held that in particular the absence of management overlap between Eni and the daughter companies, was not enough to rebut the presumption of the companies being a single economic unit. In competition law, therefore, the corporate veil may be quite easily pierced in a holding context, which undoubtedly is not the approach which many Member States take outside of the competition law area.
The waters therefore on the piercing of the corporate veil other than in the area of competition law, remain quite deep. This has an impact on the conflicts area, in particular in the application of the Rome II Regulation and the debate on corporate social responsibility, on which I have reported before on this blog.
postscript: point made in e.g. the UKSC on 12 June 2013, in Petrodel v Prest (a matrimonial assets case which was decided on the basis of trust), where Lord Neuberger stated obiter “if piercing the corporate veil has any role to play, it is in connection with evasion”.
Lord Sumption’s take was “there is a limited principle of English law which applies when a person is under an existing legal obligation…which he deliberately evades or whose enforcement he deliberately frustrates by interposing a company under his control. The court may then pierce the corporate veil for the purpose, and only for the purpose, of depriving the company or its controller of the advantage that they would otherwise have obtained by the company’s separate legal personality“. He added ‘The principle is properly described as a limited one, because in almost every case where the test is satisfied, the facts will in practice disclose a legal relationship between the company and its controller which will make it unnecessary to pierce the corporate veil.’
Lord Clarke, agreeing with Lord Mance and others, stated “the situations in which piercing the corporate veil may be available as a fall-back are likely to be very rare”.