Neither should users who refuse permission for their data to be merged be shut out of Facebook services as a result, the Federal Competition Office (FCO) ruled.
"In future, Facebook will no longer be allowed to force its users to agree to the practically unrestricted collection and assigning of non-Facebook data to their Facebook user accounts," FCO chief Andreas Mundt said in a statement.
"If users do not consent, Facebook may not exclude them from its services and must refrain from collecting and merging data from different sources."
Officials have been looking into Facebook since mid-2016, charging that the Silicon Valley giant uses other networks - like subsidiaries Instagram and Whatsapp, as well as Twitter and other websites - to collect masses of information about users without their knowledge. That data then provides the foundation for Facebook's advertising profits.