European Union privacy regulators told WhatsApp to “pause” its sharing of user data with parent Facebook as the policy is investigated, while also issuing a warning to Yahoo about an earlier breach.

According to several publications, the Article 29 working party wrote to Facebook saying it had serious concerns about WhatsApp’s recent policy change, under which it would share user data with its parent company, including phone numbers.

In the letter, the group, made up of privacy experts from the EU’s 28 member states, “requested WhatsApp to communicate all relevant information to the Working Party as soon as possible and urged the company to pause the sharing of users’ data until the appropriate legal protections can be assured”.

A WhatsApp spokeswoman has since responded, stating it was “working with data protection authorities to address their questions”, reported The Wall Street Journal.

The EU’s warning comes after it said in August, shortly after Facebook announced the policy change, it would follow the move “with great vigilance”.

Several national privacy watchdogs have taken a hard line on the issue, while Facebook has maintained the policy complies with European data protection law.

With regards to Yahoo, the EU body also expressed concerns about a 2014 network breach, which first came to light in September, and affected up to 500 million users.

The revelation was followed by allegations that the company had also been scanning user emails at the request of a US agency.

The EU told Yahoo it must cooperate with “all upcoming national data protection authorities’ inquiries and investigations”, and communicate all aspects of the breach to the EU authorities, reported Reuters.