"The German Federation of Journalists recommends journalists to avoid until further notice the use of search engines and e-mail services from Google and Yahoo for their research and digital communication," the union said in a statement.
The warning follows what it dubbed "scandalous" reports of interception of both companies' web traffic by the US National Security Agency (NSA) and Britain's GCHQ.
Michael Konken, head of the union which represents about 38,000 journalists said that there were much safer alternatives for both searches and email. He said that searches made by journalists are just as confidential as the contact details of their sources and the contents of their communication with them.