WhatsApp’s decision to "synchronise" data with parent company Facebook will face a Spanish probe.

It comes after a German regulator recently ordered the Mark Zuckerberg-run company to kill the data it holds on millions of WhatsApp users in the country.

Spain’s data protection agency AEPD announced that it will investigate the new data-sharing strategy revealed by the messaging service in August. When WhatsApp was taken over by Facebook in 2014, it promised not to share users’ data and the U-turn has provoked widespread anger.

The watchdog advised users to read the new terms and conditions carefully before clicking the "I agree" button. It also gave users practical advice on how to change their settings as its investigation gets under way.

Last week, a German DPA ordered Facebook to delete all the data of Germany’s 35 million WhatsApp users. "After the acquisition of WhatsApp by Facebook two years ago, both parties publicly assured that data will not be shared between them," said Hamburg data protection commissioner Johannes Caspar. "The fact that this is now happening is not only misleading of their users and the public, but also constitutes an infringement of national data protection law."

Italy's data watchdog Garante Privacy has also launched a formal probe. It said last week that it was particularly concerned that users' rights "to revoke their consent or object appear to only be exercisable within a limited time span from when a company notice is sent to single devices."

When WhatsApp announced that it would share data with Facebook, the UK’s information commissioner Elizabeth Denham said she would look into it.

"The changes WhatsApp and Facebook are making will affect a lot of people. Some might consider it’ll give them a better service, others may be concerned by the lack of control. Our role is to pull back the curtain on things like this, ensuring that companies are being transparent with the public about how their personal data is being shared," she said.

However, the Information Commissioner's Office had no update on whether any formal investigation was being mulled when quizzed by Ars on Thursday.

Companies aren't required to get approval from the ICO before changing privacy policies, but data protection authorities have the power to investigate any breaches in data protection law. The steering body made up of all of the European Union’s data regulators, the so-called Article 29 Working Group, has discussed the issue and will help to coordinate national investigations.

In the US, the Federal Trade Commission has received complaints about the WhatsApp/Facebook data swap from The Electronic Privacy Information Center (EPIC) and the Center for Digital Democracy.