In a letter signed by 69 MEPs and another 20 politicians from EU member states, the German government is accused of "allowing a major rift between EU member countries to fester at a time when the EU needs cohesion more than ever before".
"We ask you, Madam Chancellor, that your government reconsiders and changes its policy on Nord Stream 2," the MEPs said.
"Stop blocking the work on the Gas Directive. Support the course set by the European Commission and the European Parliament. Let Russia's President know that Germany will stand by its EU partners and by Ukraine. Choose the European way, not the 'Germany first' way," they said.
The MEPs say that by relying on Russia's gas giant Gazprom for up to 80 percent of its gas supplies, Germany would reduce its own energy independence, which would have a negative impact on the energy security of the EU.
They criticize Berlin for "ignoring the security concerns that countries around the Baltic, NATO and the United States of America have been warning against".
"Germany, by acting short-sightedly, would undermine the solidarity principle within the EU. That is the very principle on which the EU must be based, if it is to be successful. Your government is not following the right priorities, Madam Chancellor. Please, do change course!", the letter concludes.
Some fear that the Russian-German joint project will give Russia excessive control in Europe, hurting Poland and Ukraine in particular. Merkel visited both countries last week, and experts say that the pipeline project issue was on the agenda of her meeting with Ukrainian President Petro Poroshenko.
The 10-billion-euro, 1,230-kilometer Nord Stream 2 is expected to be completed by early 2020. The pipeline will run adjacent to the existing Nord Stream and will double its capacity.