ECB's bond-buying plan referred to Europe's top court
An emergency measure that was credited with stabilising the euro has been referred to Europe's top court.
On Friday, Germany's constitutional court said that the European Central Bank's (ECB) bond-buying scheme could be "incompatible" with EU law.
The European Court of Justice will now decide the legality of the so-called debt "backstop", introduced in 2012.
Although the ECB has not used the emergency power, its existence calmed turmoil in European financial markets.
When he announced the Outright Monetary Transactions (OMT) programme, ECB President Mario Draghi said he would do "whatever it takes" to save the single currency.
But the German court has said there was good reason to think the OMT violated a ban on the bank funding governments.
In a statement, the court added: "There are important reasons to assume that it exceeds the European Central Bank's monetary policy mandate and thus infringes the powers of the member states."
However, the court also said it "considers it possible that if the OMT decision were interpreted restrictively" it could conform with EU law.
Even though the OMT has not yet been used, confidence was restored to the markets at the suggestion that the ECB could buy unlimited amounts of a country's debt if investors pulled out.
If it were declared illegal, there could be big implications for the bloc and its single currency.
The euro fell to a session low against the dollar in response to the court's finding.
However, it's thought unlikely the European Court of Justice (ECJ) will block the OMT policy.
"The (OMT's) chances are better in Luxembourg than in Karlsruhe," said Bert Van Rossebeke, from the Centre for European Politics in Freiburg.
Gunnar Beck, a European law expert at the University of London, said it would be unusual for the ECJ to obstruct a large, bloc-wide measure.
"Practically speaking, the court is not an independent organisation but is pre-disposed to interpret legal questions in the interest of the European Union," he added.
"The court of justice doesn't take account of national sensibilities... There is no doubt of the outcome now."
Analysts say it could take the ECJ up to two years to rule on the OMT programme.