Article 267 TFEU provides for a method of constitutional dialogue between Member States and the Court of Justice of the European Union (CJEU): the preliminary reference procedure. According to Bosch , further integration required a procedure in which difficult problems could be solved. Therefore, under Art 267 TFEU, Member States may ask the CJEU for help in clarifying and interpreting EU law in the interest of effective judicial protection. During a case in a court of a Member State, when faced with a difficult question concerning EU law, that court may make a preliminary reference to the CJEU, who will usually answer the court’s questions. Following the CJEU’s answer (judgment), the national court may then deliver its ruling.
Decision to refer
The CJEU is flexible as to responding to preliminary references. In Irish Creamery Association v Government of Ireland , the CJEU said that a national court may refer a question at any time as to prevent interference with national processes. However, there are a few restrictions. The CJEU may refuse to respond to questions if they are referred from bogus litigation, as occurred in Foglia v Novello I  or if the questions referred are not related to the law of the national dispute: in Bacardi-Martini v Newcastle United Football Club , the CJEU refused to give a ruling on the compatibility of French law with EU law in an English dispute.
Choice of questions
The questions given to the CJEU by a national court are to be decided upon by the national court. However, the CJEU may reword or extrapolate from the questions given, according to Costa v ENEL .
Subject of reference
The CJEU may only act within the competence of the EU, as it is an institution of the EU. However, as illustrated by PreussenElektra , as long as there is some connection with the competence of the EU (such as state aid), even without a cross-border element, the CJEU will set out a substantive answer to the national court’s questions.
Competence to refer
According to Gabalfrisa , any genuine court or tribunal, if recognised by the state, may initiate a preliminary reference. The court or tribunal must make decisions of a judicial nature, according to Victoria Film .
Obligation to refer
As stated in Foto-Frost , only the CJEU may decide whether EU law has been breached, therefore it is advisable to refer. This was echoed by [Lord] Bingham in ex p Else , who said that if in doubt, a court should make a preliminary reference. Lyckeskog  maintained that even Supreme Courts must still refer to the CJEU on EU law issues. Only CILFIT  limits the need to refer, dispensing with the obligation to refer if: the reference would not affect the outcome of the national case; the question has been litigated before or the answer to the preliminary reference is obvious.