When messaging app WhatsApp was acquired by Facebook in 2014, WhatsApp co-founder Jan Koum promised the deal wouldn't affect users' privacy.
WhatsApp said it will also share more information about its users with the "Facebook family".
WhatsApp keeps the policy change somewhat hidden, but there are two options.
Popular messaging service WhatsApp said it would start sharing users' phone numbers with parent Facebook Inc, marking a notable shift in its stance on privacy.
The data would be used to show more targeted ads on Facebook, and not on WhatsApp itself.
In its FAQs, while answering the questiong, 'Will there be ads on Whatsapp now?' the company said that you may receive flight status information for upcoming travel, a receipt for something you purchased, or a notification when a delivery will be made.
WhatsApp tested making business by dropping its $1 token fee for some of its users earlier this year through the service.
The new changes to the terms and conditions allow Facebook to see the phone number that people use with their WhatsApp account.
The people at WhatsApp were quick to point out that your encrypted messages will stay private, meaning you're the only person that can read them.
The company assured its users that 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".
It's worth noting the details included in the agreement: your phone number, profile name and photo, online status and status message, last seen status, and receipts. "In fact, Facebook will not use your WhatsApp messages for any goal other than to assist us in operating and providing our Services".
The company will be testing the new features over the next few months. Scroll all the way down and uncheck the box that will share your WhatsApp info with Facebook.
The changes will also help Facebook fight spam accounts and better understand how people use the apps. WhatsApp has always been proponent of user privacy, a focus that attracted a fair few users to the service, and this will nearly certainly be seen by some as WhatsApp stepping back from the strict privacy guidelines it once held.
But by sharing your data with the social media site, it will slightly change your Facebook experience.