Facebook and Google have both run into European privacy concerns before. Could this be the most serious challenge yet?
The data protection commissioner in Schleswig Holstein, Thilo Weichert, said the 'Like' button leads to profiling that violates German and European law.
Facebook claims in response that it is in full compliance with European data protection laws.
If Weichert is correct, the 'Like' button would be in violation of the same European laws in the UK.
Weichert said technical analysis by his office shows Facebook breached the law by passing content data to the social network's servers in the U.S.
'Whoever visits facebook.com or uses a plug-in must expect that he or she will be tracked by the company for two years,' hhe said.
'Facebook builds a broad individual and for members even a personalised profile.'
A Facebook spokesman agreed the company can see 'information such as the IP address' of users who visit a site with a 'Like' button.
'We delete this technical data within 90 days,' said the spokesman, according to a report on the Daily Mail website. "That is in keeping with normal industry standards.'
Weichert's office ordered website owners in Schleswig-Holstein, the country's most northerly state whose capital is Kiel, to 'immediately stop the passing on of user data to Facebook in the USA by deactivating the respective services' and threatened to take legal action if they fail to comply.
He also urged Internet users in general to 'keep their fingers from clicking on social plug-ins' and 'not set up a Facebook account' to avoid being profiled.
Germany's privacy laws are strict and there have been earlier clashes with international Internet giants, such as Facebook and Google, said the Mail.
Last year Google allowed Germans opposed to its Street View mapping system to blur images of their homes. In January Facebook granted members more control over their email address books, after a disagreement over its 'Friend Finder' service.