"We consider the saving of data from third parties, in this context, to be against data privacy laws," Caspar said in a statement.
Facebook has until Aug. 11 to respond formally to the legal complaint against it. Its response will determine whether the case goes further.
Germans are protected by some of the world's most strict privacy laws, which lay out in detail how and how much of an individual's private information may be accessed by whom.
Germany also has launched an investigation into Google Inc. over its Street View mapping program.
In April, Facebook changed its privacy settings to allow users to block access to the contacts listed in their e-mail, but Caspar argues that the previously saved contacts have not been erased and are being used for marketing purposes.
"It is a system that is designed around making it possible for Facebook to expand, for its own benefit," Caspar said in a telephone interview.
He said his office had received complaints from "many" people who had been contacted by Facebook after it obtained their names and e-mail addresses through people listing them as a contact.
He could not give a specific number, but said that it indicated third parties' data had been obtained by Facebook had been saved for future use.
"Given that several million people in Germany alone are members, this is a very unsettling notion," he said.
Germany's consumer protection minister, Ilse Aigner, said last month that she plans to give up her Facebook account, arguing that it still wasn't doing enough to protect users' data.