Information collected by Jehovah's Witnesses while engaged in door-to-door preaching is subject to data protection laws, the Court of Justice of the European Union ruled on 10 July 2018 in an appeal from a Finnish court.
The information included people's names and addresses, and whatever they said about their religious beliefs. This came within the scope of personal data.
Tietosuojavaluutettu v Jehovan todistajat uskonnolinen yhdyskunta. CJEU. Case C-25/17. The Times 24 September 2018 [18.09]