KEY POINTS
  • The European Central Bank was quick to react, arguing that it follows decisions taken by the European Court of Justice — not national courts.
  • However, the German ruling has sparked an unprecedented legal minefield and has led to new questions about the future of the euro zone.
A euro currency symbol sits on display in the visitor centre at the European Central Bank (ECB) building in Frankfurt, Germany.

The stability of the euro zone is once again under scrutiny after the German Constitutional Court issued a decision last week that surprised financial markets and policymakers in Europe.

The highest court in Germany said last Tuesday that parts of the European Central Bank's (ECB) actions were illegal under German law. The court said one of the ECB's tools — its quantitative easing program — did not respect "the principle of proportionality" and that the German central bank and government should have challenged the central bank in this regard.