The concern arises when Facebook accountholders use the site's invitation and address book sync features to upload data about non-users, then Facebook stores this data. Since some of these individuals do not belong to Facebook, at no time have they granted permission for the site to use or save private data -- such as phone numbers and e-mail addresses, the Hamburg commissioner said.
"We consider the saving of data from third parties, in this context, to be against data privacy laws," said Johannes Caspar, head of the Hamburg office for data protection, in a statement.
The legal action could result in a fine of tens of thousands of Euros, he said. "Many" people were contacted by Facebook after the site received their names and e-mail information from friends or colleagues on the social networking site, Caspar told the Associated Press. He declined to provide an exact number of complainants.
Facebook, which has until Aug. 11 to respond, confirmed receipt of the letter. "We are currently reviewing it and will readily respond to it within the given timeframe," Facebook told the AP.
Although Germany is known for its tough privacy-protection laws, it is not the only nation scrutinizing Facebook's use of user data. Canada, Britain, and Switzerland, for example, are looking into how the company safeguards and uses peoples' information.
On its home turf in the United States, Congress is looking into privacy protections on Facebook and other social networks to determine whether more government regulation is necessary.
Facebook has come head-to-head with a number of vocal and diverse government, privacy, and consumer advocates displeased with the company's many and frequent policy changes. Facebook responded to a spate of letters and complaints in late spring by revising and simplifying its policies, but in mid-June, 10 advocacy groups submitted an open letter to Facebook requesting six more changes.
"We are glad to see that Facebook has taken steps in the past weeks to address some of its outstanding privacy problems," the letter said. "However, we are writing to urge you to continue to demonstrate your commitment to the principle of giving users control over how and with whom they share by taking these additional steps."
Facebook quickly rebutted this request by reminding the advocacy groups of the recent changes and confirming its commitment to participating in ongoing talks about privacy and consumer protection.
On June 7, the site launched its dedicated Facebook and Privacy page, the company's most recent attempt at providing users with access to information on how to best protect their personal information.