According to the opinion of the Advocate General Pedro Cruz Villalón, published 12 December 2013, the Directive 2006/24/EC is as a whole incompatible with the requirement, laid down in the Charter of Fundamental Rights, that every limitation on the exercise of a fundamental right must be provided for by law. The Directive itself should already contain the principles that would govern the minimum guarantees for access to the data, retention and use of the data. These guarantees, and their establishment, application and review of compliance, need to be defined in the Directive itself. Further, the Advocate General deems the Directive not proportionate because it obligates the Member States to retention for a maximum period of two years. The Advocate General fails to see a justification for retaining the data for longer than one year.

However, Advocate General Cruz Villalón does not recommend a finding of immediate invalidity to the European Court of Justice. Rather, the effects of such finding should be suspended pending the adoption of measures that remedy the invalidity by European legislature, within a reasonable time frame. The objectives of the Directive itself are not illegitimate, but the measures required to reach these objectives are incompatible with the fundamental rights of the citizens.

In Germany, the Federal Constitutional Court had already declared that the national implementation of the Directive does not conform with the German Constitution, which rendered the implementing legislation invalid. While the potential parties to the coalition have already committed to a re-implementation of the Directive in the draft coalition agreement, it remains to be seen whether they will step back from such plan after the opinion of the Advocate General and at least wait for the decision of the European Court of Justice, which usually follows the opinion of the Advocate General.