Opponents of the trade deal want the judges in the Federal Constitutional Court in Karlsruhe to compel the German government to vote 'no' on the deal when it is deliberated by the European Council on October 18th.
If the treaty is approved by the European Council, it will be signed at the end of the month. If it is then voted through the European Parliament, it will be almost immediately implemented.
The consumer watchdog Foodwatch, along with the activist organizations Campact and Mehr Demokratie (More Democracy), mobilized more than 125,000 co-plaintiffs, making it the single largest group of plaintiffs in the history of the Constitutional Court.
According to the plaintiffs, the immediate implementation of the deal will mean that it will be turned into reality before the Bundestag (German parliament) and the parliaments of other member states have had a chance to debate and vote on the treaty.
“The German government and the EU have made it clear from the beginning that they plan to push the deal through, even against the will of their own citizens - and now they are doing that,” said Klaus Ernst, deputy leader of Die Linke (the Left party) in the Bundestag.
Vice-Chancellor and Economy Minister Sigmar Gabriel is set to defend the trade deal at the hearing.
The panel of judges led by Andreas Voßkuhle will deliberate directly after the hearing and is set to announce a verdict at 10am on Thursday.
At first the judges will only rule on whether a preliminary application of CETA could lead to disadvantages being created that could not be reversed later.
The total of five suits brought by the plaintiffs against the treaty will be considered individually at a later point.
“Through a preliminary implementation of the treaty, permanent realities will be created,” warned Foodwatch head Thilo Bode.
Critics also claim the deal puts consumer and environmental protection at risk. The government claims that a trade area with almost no import duties will be an economic boon to Germany.
In September more than 160,000 people protested in seven German cities against CETA and TTIP, a similar free trade deal which is currently being negotiated between the EU and the United States.