The northern German city-state's data protection agency suspects that the social networking website places a so-called "cookies" on users' internet browsers that can keep tabs on them for two years after abandoning Facebook. The cookie can also be read by plug-ins on other websites, according to the organisation.
“Arguments that all users have to remain known after they leave Facebook to guarantee the service's security are not acceptable,” the Hamburg data protection director Johannes Caspar said on his agency's website.
Facebook has always acknowledged that it places cookies on computers. But it insisted in a statement that it was not tracking users' movements across the web and it was seeking an “open channel of communication” with Caspar and his colleagues.
Internet services, such as Google Street View and Facebook, have come under increasing fire from German officials in recent months, amid accusations that they're consistently breaking the country's privacy laws.
Schleswig-Holstein officials have been particularly aggressive in pursuing Facebook, even declaring its “like” button violates the law.
In response, Facebook has said it is agreeing to a voluntary code of conduct in Germany to protect user data.