Irish data privacy waIreland hit Facebook's WhatsApp with a record €225 million ($266 million) fine on Thursday following an inquiry into the messaging app's transparency around sharing personal data with other Facebook companies.
WhatsApp said the fine was "entirely disproportionate" and that it would appeal.
Ireland's Data Privacy Commissioner (DPC), which is the lead data privacy regulator for Facebook within the European Union, said the issues related to whether WhatsApp conformed in 2018 with EU data rules about transparency.
"This includes information provided to data subjects about the processing of information between WhatsApp and other Facebook companies," the Irish regulator said in a statement.
A WhatsApp spokesperson said in a statement that the issues in question related to policies in place in 2018.
"WhatsApp is committed to providing a secure and private service. We have worked to ensure the information we provide is transparent and comprehensive and will continue to do so," the spokesperson said.
"We disagree with the decision today regarding the transparency we provided to people in 2018 and the penalties are entirely disproportionate," the spokesperson's statement said.
Ireland's DPC takes the lead on data privacy for Facebook because the company's regional headquarters is in Dublin.
The DPC has been criticised in the past by other European regulators for taking too long to reach decisions involving tech giants and for not fining them enough for any breaches.
Data regulators from eight other European countries triggered a dispute resolution mechanism after Ireland shared its provisional decision in relation to the WhatsApp inquiry, which started in December 2018.
In July, a meeting of the European Data Protection Board issued a "clear instruction that required the DPC to reassess and increase its proposed fine on the basis of a number of factors contained", the Irish regulator said.
"Following this reassessment the DPC has imposed a fine of €225 million on WhatsApp," it said.
The Irish regulator also imposed a reprimand along with an order for WhatsApp to bring its processing into compliance by taking "a range of specified remedial actions".
The Irish regulator had 14 major inquiries into Facebook and its subsidiaries WhatsApp and Instagram open as of the end of last year.