BRUSSELS (Reuters) - Jehovah’s Witnesses must obtain consent from people before they take down their personal details during door-to-door preaching in order to comply with EU data privacy rules, Europe’s top court ruled on Tuesday.

The case arose after Finland in 2013 banned Jehovah’s Witnesses from collecting personal data during door-to-door visits.

The U.S.-based Christian denomination, which says it has more than 8 million followers worldwide, challenged the decision, saying that its preaching should be considered a personal religious activity and as such the notes taken down during such visits are also personal.

A Finnish court subsequently asked the Luxembourg-based Court of the Justice of the European Union (ECJ) for advice, which said on Tuesday that such religious activity is not covered by exemptions granted to personal activity.

“A religious community, such as the Jehovah’s Witnesses, is a controller, jointly with its members who engage in preaching, for the processing of personal data carried out by the latter in the context of door-to-door preaching,” judges said.

“The processing of personal data carried out in the context of such activity must respect the rules of EU law on the protection of personal data.”

Under EU data protection rules, a controller determines how and why the personal data is processed.

Jehovah’s Witnesses differ from mainstream Christianity in a number of their beliefs, including rejecting the doctrine of the Trinity and opposing blood transfusions and military conscription.