The ruling also marked the first time that the top court in the German city of Karlsruhe has gone against findings by the European Court of Justice.

Top German judges raised concerns back in 2017 that one part of the bond-buying programme, the Public Sector Purchase Programme (PSPP), could engage in economic policy and government financing, both of which the ECB is prohibited from doing.

The programme was used to buy government bonds and other securities worth approximately 2.6 trillion euros (2.9 trillion dollars) between March 2015 and the end of 2018, with the aim of boosting the economy. More than 2.1 trillion euros in purchases were made as part of the PSPP.

The panel of top judges granted several constitutional complaints directed against the PSPP, finding that the ECB decisions taken under the scheme “exceed EU competences.”

The Bundesbank, Germany’s central bank and a key driver in ECB purchasing power as the eurozone institute’s top shareholder, can continue contributing to the asset purchases for a maximum of three months, after which the German government and parliament will have to get involved.

It will be up to Berlin’s cabinet and lawmakers to assess the scope of the purchases going forward, after the judges found that they had previously failed to keep the ECB in check.

The judgement could “at first appear irritating” given the economic challenges posed by the coronavirus pandemic, said Constitutional Court president Andreas Vosskuhle. But he stressed the need for a firm legal basis “to overcome the crisis.”

A statement from the court said the decision “does not concern any financial assistance measures taken by the European Union or the ECB in the context of the current coronavirus crisis.”

The ECB is relying on further bond-buying measures as the pandemic wreaks havoc with the world economy, recently unveiling a 750-billion-euro Pandemic Emergency Purchase Programme (PEPP), while current asset purchases are to be boosted by around 20 billion euros by the end of the year.

German Finance Minister Olaf Scholz insisted that eurozone solidarity is not endangered by the ruling.

“At a time when the coronavirus crisis is making great demands of us, the single currency and common monetary policy give us the cohesion we need in Europe,” Scholz said in Berlin.

“The Bundesbank may continue to participate in the joint purchase programme for the time being,” he added.

With its ruling, German Constitutional Court went against a decision issued by the European Court of Justice in Luxembourg in December 2018, which said that the ECB’s decision to buy government bonds was valid and within its mandate.

The German judges ruled that the ECJ judgement was “not comprehensible.”

The European Court of Justice declined to comment on Tuesday, saying that it does not make statements on national court decisions.

The European Commission reacted by stressing that rulings from the top EU court have the final say.

“We reaffirm the primacy of EU law and the fact that the rulings of the European Court of Justice are binding on all national courts,” spokesperson Eric Mamer said.

The German ruling won’t spell an end to the ECB’s bond-buying scheme, according to Commerzbank economist Joerg Kraemer.

“This may be an affront to the ECB. But with its armada of economists and legal experts, the ECB can easily overcome such a problem,” Kraemer said.

On the other hand, Clemens Fuest, president of the Ifo research institute, said the ruling would limit the ECB’s ability to support highly-indebted member states through bond purchases.

“In turn, this puts increasing pressure on euro-area governments to provide assistance to individual member states in the form of fiscal policy instead of relying on the ECB,” he noted.

The central bank’s governing council is to hold an extraordinary telephone conference later Tuesday to discuss the development, an ECB spokesman told dpa.