When Facebook purchased WhatsApp in 2014, the messaging service vowed that its focus on user privacy wouldn't change. Last week, an update to the company's terms-of-service appeared to backtrack on this pledge, something that privacy groups and watchdogs on both sides of the Atlantic are unhappy about.

Two groups voicing their concerns are the Electronic Privacy Information Center (Epic) in the US and the UK's Information Commissioner's Office (ICO).

The ICO is still in the middle of investigating the matter, but Epic has already filed a complaint with the Federal Trade Commission (FTC) against WhatsApp and Facebook. The organization says the update violates the FTC act that prohibits "unfair or deceptive trade practices." Specifically, this refers to WhatsApp's promise in 2014 that it wouldn't share personally identifiable information such as phone numbers. Epic is also critical of the fact that users have to opt-out of sharing their data, rather than the system being opt-in.

WhatsApp defended its policy change in a blog titled "Setting the record straight." The company says it needs to share user information with Facebook as a way of testing new features, such as the ability for businesses to communicate with customers.

Sharing account information with Facebook will also help the social network make better friend suggestions and deliver more relevant ads. WhatsApp said this would also enable it to "fight spam and abuse, and improve experiences across our services and those of Facebook and the Facebook family."

There's still time left to opt-out of having certain account information shared with Facebook to "improve ads and products experiences."