WhatsApp in January introduced a privacy policy which allows it to share some data with Facebook and other group firms.
It said the changes permit users to message with businesses and would not affect personal conversations.
The European Consumer Organisation (BEUC) and eight of its members criticised the changes and filed complaints with the European Commission and the European network of consumer authorities, saying WhatsApp was unfairly pressuring users to accept its new policies.
"The content of these notifications, their nature, timing and recurrence put an undue pressure on users and impair their freedom of choice. As such, they are a breach of the EU Directive on Unfair Commercial Practices," the groups said in a joint statement.
"WhatsApp has failed to explain in plain and intelligible language the nature of the changes... This ambiguity amounts to a breach of EU consumer law which obliges companies to use clear and transparent contract terms and commercial communications," they said.
Facebook said BEUC has got the issue wrong.
"BEUC's action is based on a misunderstanding of the purpose and effect of the update to our terms of service," a spokesperson said.
"The update does not expand our ability to share data with Facebook, and does not impact the privacy of your messages with friends or family, wherever they are in the world. We would welcome an opportunity to explain the update to BEUC to clarify what it means for people."
The consumer groups urged the European network of consumer authorities and EU data protection authorities to work together to address these privacy and consumer rights concerns.
