A supermarket in Rochdale, England | Christopher Furlong/Getty Images German and British business groups call for clarity in Brexit talks German exports to the UK dropped by 3 percent in the first half of the year.

The German and British chambers of commerce Monday called for Brexit negotiators to bring clarity for businesses as the third round of Brexit talks resumes in Brussels.

The British Chambers of Commerce (BCC) and the Association of German Chambers of Commerce (DIHK) said in a joint call that political leaders should build “an atmosphere of mutual trust and constructive dialogue,” to deliver clarity and certainty for trading businesses across Europe.

Martin Wansleben, CEO of the Association of German Chambers of Industry and Commerce (DIHK), said businesses are worried about the negative impact of Brexit.

"The terms of exit are still completely unclear. Many of our members are reporting that they are already shifting investments away from the U.K. in anticipation of these barriers," Wansleben said.

“The first effects of the Brexit vote are already being observed: German exports to the United Kingdom were down by 3 percent in the first half of this year compared to the first half of last year, whilst exports to the EU increased by 6 percent in the same period," he added.

A DIHK survey suggests that the business outlook for companies trading with the U.K. is worsening, as a result of expectations that costs and bureaucratic hurdles will increase.