A British vote to leave the European Union would shake the bloc and require a concerted effort to ensure its stability, warns Germany and France. Foreign Minister Frank-Walter Steinmeier said on Wednesday.

Speaking at a news conference, French Foreign Minister Jean-Marc Ayrault, Steinmeier said they both hoped that Britons would vote to stay in the EU in their June 23 referendum. “That would be the right decision to make,” he said.

 “A vote to leave would shake the union. It would not just carry on as 28 (members) minus one. It would require concerted efforts to ensure that the union holds together and that a decades-long, successful integration effort does not end in disintegration,” he said.

German Foreign Minister Frank-Walter Steinmeier, who also attended the new conference, backed up Steinmeier’s comments.

He said France and Germany had a special role to play since they had helped to found the European Community and had experienced the fruits of successful integration for perhaps the longest period.

“We both belong to those who say ... we cannot lapse back into a nationalism that pits one European state against another”.

He said both countries would work to ensure the EU’s continued survival and success even if Britons voted to leave.

France and the then-West Germany are founder members along with the Netherlands, Belgium, Luxembourg and Italy, of what eventually turned into the EU. Britain joined in 1973 but has long resisted steps towards closer integration, remaining outside the euro currency and the passport-free Schengen zone.

German economic institute DIW said on Wednesday Britain’s exit from the EU would probably drive export tariffs higher, reducing German trade and knocking half a percentage point off growth in Europe’s biggest economy next year.

With a total trade volume of 127.5 billion euros, Britain is Germany’s fifth biggest trading partner behind the United States, France, the Netherlands and China. For Britain, Germany is the most important trade partner, ahead of the United States.

Several recent opinion polls have shown the “Leave” campaign taking the lead in Britain’s referendum campaign, despite warnings from Prime Minister David Cameron, the Bank of England and others that Brexit could cause significant economic disruption.