The principle of primacy of EU law plays an important role at the domestic level of the EU Member States. EU law must be directly applied not only by courts, but also by administrative bodies. This is particularly the case when there is settled ECJ case law on a particular legal issue. One example of the application of this principle, in combination with the application of the acte clair and acte éclairé doctrines, is the retroactive application of the Spanish horizontal tax group regime.