Berlin's mayor spoke out against a planned trade agreement between Canada and the European Union on Saturday, as another German state submitted one of the largest petitions in German history in protest to the deal.
Opposition to the agreement, known as CETA, has mounted as Canadian and EU leaders prepare to sign the agreement in October once it has been approved on both sides of the Atlantic.
"I have serious concerns about CETA," Berlin Mayor Michael Mueller told the Berliner Morgenpost daily.
"Unless there are dramatic developments and improvements over the next few weeks, I don't think we can support this in Berlin," Mueller said, breaking ranks with his Social Democratic Party, which has previously shown strong support for the agreement.
At the same time, over 68,000 citizens in the German state of North Rhine Westphalia have taken part in one of the country's largest petitions to the constitutional court in protest against the trade deal.
Over 150 boxes each containing around 500 pages of signatures were delivered to the court in Karlsruhe on Saturday as part of a petition launched on campaign platform change.org.
Critics fear that transatlantic trade deals like CETA could allow corporations to block undesirable regulations, while negatively impacting consumer protection.