to levy a dissuasive tax. That taxes levied on products have the potential to affect consumer behaviour and thereby access to markets is obvious and even constitutes the main rationale of environmental taxation. Although not imposed at the time of importation, taxes are quite capable of discriminating against imported goods and have effects similar to those covered by Article 34. Internal taxes have even more in common with the customs duties and charges having equivalent effect which are prohibited under Article 30 TFEU. But although that Article and the Treaty provisions on discriminatory internal taxation (Article 110 TFEU) complement each other in pursuing the objective of prohibiting any national fiscal measure that is liable to discriminate against products coming from or destined for other Member States, these provisions are mutually exclusive and the same measure cannot belong to both categories at the same time.09 The determinative factor is whether the charge at issue is triggered by the fact that the products cross a border. If not it may be considered an internal tax, but not a charge having equivalent effect to a customs duty.    
Despite the similarities, a fundamental difference is that unlike quantitative restrictions and custom duties, taxes are a fully legitimate policy instrument and Member States have a considerable discretion to devise their own tax policies, including by imposing environmental taxes.131 This is often referred to as the fiscal autonomy of the Member States. 132
What is in principle not acceptable is the imposition of internal taxes in a way which affords protection to domestic products at the expense of those imported from other Member States. This situation is addressed in Article 110 TFEU, which aims to ensure free movement of goods between the Member States by the elimination of all forms of protection which may result from the application of internal taxation that discriminates against products from other Member States.°3
Article 110, which consists of two paragraphs which deal with partly different situations, reads as follows:
No Member State shall impose, directly or indirectly, on the products of other Member States any internal taxation of any kind in excess of that imposed directly or indirectly on similar domestic products.
Furthermore, no Member State shall impose on the products of other Member States any internal taxation of such a nature as to afford indirect protection to other products.
Hence both higher levels of internal taxation on imported products compared to similar domestic products and other kinds of taxation imposed on the products of other Member States which have a protective effect are prohibited. The Court of Justice has made clear that a system of taxation is compatible with Article 110
The applicability of Article 110 is wide. It is not only taxes in the narrow sense on products as such or on their use, but also other charges, that may be covered. In Stadtgemeinde Frohnleiten the Court of Justice found that a levy on the operator of a waste disposal site the rate of which depended at least partly on the weight and nature of the waste deposited was covered by this Article.135
Of vital importance with respect to environmental taxes is, however, the fact that each Member State is free to establish a tax system which differentiates between certain products, even products which are similar within the meaning of Article 110 (1), on the basis of objective criteria, including the manner in which a product is produced and the raw materials used for its production. In order to be allowed, such differentiation must pursue objectives which are themselves compatible with the requirements of the Treaties and EU secondary law, and the detailed rules must be such as to avoid any form of discrimination, direct or indirect, against imports from other Member States or any form of protection of competing domestic prod- ucts.136 Genuine environmental concerns are therefore generally not problematic as a ground for differentiation of taxation. The important point is that no distinction must be made based on the origin of the goods and that care must be taken to devise the tax so that no protective effect is otherwise afforded.
C Barnard The Substantive Law of the EU: The Four Freedoms (Oxford University Press, 2013)
M S Jansson and H Kalimo ‘De Minimis meets “Market Access”: Transformations in the Substance—and the Syntax—of EU Free Movement Law?’ (2014) 51 Common Market Law Review 523—58
I Lianos ‘Shifting Narratives in the European Internal Market: Efficient Restrictions of Trade and the Nature of “Economic” Integration’ (2010) 21 European Business Law Review 705—60
G Mathisen ‘Consistency and Coherence as Conditions for Justification of Member State Measures Restricting Free Movement’ (2010) 47 Common Market Law Review 1021—48
N de Sadeleer EU Environmental Law and the Internal Market (Oxford University Press, 2014)