By Jonathan Davies
The German Chambers of Commerce and Industry has warned the UK that leaving the European Union would be "disastrous" for both countries.
The organisation's deputy chief executive Volker Treier told the BBC that German businesses are "astonished" that the UK is holding a referendum.
Prime Minister David Cameron is currently on a tour of Europe, canvassing support for his proposed reforms from European leaders.
He received a boost from French President Francois Hollande, who indicated that he would be willing to listen to proposals.
Mr Cameron meets German Chancellor Angela Merkel today (Friday) to discuss his proposals. Germany is likely to be the UK's biggest enemy in securing reform. And Mr Treier believes Ms Merkel should not give any concessions.
He said that the near 400,000 German people who live and work in the UK would be unsettled by uncertainty surrounding their jobs. And Mr Treier warned that German companies would consider pulling out their investments in the UK.