It is the largest fine ever from the Irish Data Protection Commission, and the second-highest under EU GDPR rules.
Facebook, which owns WhatsApp, has its EU headquarters is in Ireland, and the Irish regulator is the lead authority for the tech giant in Europe.
WhatsApp said it disagrees with the decision, and the severity of the fine, and plans to appeal.
The fine relates to an investigation which began in 2018, about whether WhatsApp had been transparent enough about how it handles information.
