WhatsApp has been criticised by campaigners after it backtracked on a pledge to not change its privacy policy when it was bought by Facebook in 2014.

The US-based Electronic Privacy Information Center (Epic) has claimed the social media firm has violated a Federal Trade Commission (FTC) consent order after it announced it would begin sharing user information such as phone numbers, profile data, status message and online status with Facebook.

Under the Federal Trade Commission Act, firms are forbidden from “unfair or deceptive trade pratices”.

Epic said it has filed a complaint against Facebook and WhatsApp with the FTC for lying to users during the 2014 sale when they promised the smaller company would never share “personally identifiable information”.

WhatsApp has defended the move saying it needs to share some data with Facebook to help test its new features - such as new services where users can receive fraud notifications from banks or flight delay information from airlines.

In an official blog post announcing the changes it said: “By coordinating more with Facebook, we'll be able to do things like track basic metrics about how often people use our services and better fight spam on WhatsApp.

“And by connecting your phone number with Facebook's systems, Facebook can offer better friend suggestions and show you more relevant ads if you have an account with them.”

The company said its “belief in the value of private communications is unshakeable, and we remain committed to giving you the fastest, simplest, and most reliable experience on WhatsApp”.

Users will also have 30 days to opt-out of the new sharing terms of service but critics say this only stops half of their data going to Facebook.

Epic argues that changing a company's data policies without getting the opt in consent of its users first is an "unfair and deceptive" trade practice.

The messaging service is already under fire in the UK with the Information Commissioner, who enforces the Data Protection Act, due to look into how its new policy will affect British users.

The Independent has contacted WhatsApp for comment.