Germany’s constitutional court is hearing a case brought by campaigners against a free trade deal between the EU and Canada.
An activist group has organised a petition with 125,000 signatures.
“The economy must be beneficial for the society for the sake of the community and we must reject these kind of treaties, which don’t respect democratic principles,” said one protester.
The country’s vice chancellor Sigmar Gabriel was in Karlsruhe to defend the agreement.
“This treaty is good because we will get eventually rules for globalisation. This treaty is good for Europe,” he said.
A ruling is expected on Thursday.
EU trade ministers are set to sign off on the deal next week.
And it will also need the green light from the European Parliament.
Supporters amongst MEPs say the accord will boost growth in Europe.
But if the court finds in favour of the activists, then it could scupper the planned final approval of the agreement at the end of the month.