It is to rule on whether or not the European Stability Mechanism (ESM), to which Germany is the biggest contributor, infringes the German Constitution and should not be allowed.

If the court were to rule against, which observers say is highly unlikely, it would mean the end of bailout funds and a probable run on the euro and market panic.

Chancellor Angela Merkel is expecting a ‘yes' from the court, although it may hedge its decision by attaching conditions, or even defer it until a later date.

But there are some in her own CDU party who would love the court to strike the ESM down.

"Plainly speaking, the ECB is imposing massive liability risks on the German taxpayers without any democratic legitimacy," said MP Wolfgang Bosbach.

Protesters have been picketing the court all weekend, agreeing with Bosbach that their sovereignty is being usurped, and calling for the ESM to be stopped in its tracks. And public opinion in this most pro-European of member states is turning negative towards Brussels, too.