The Turkish data protection authority said that WhatsApp no longer offered users "free will".
Turkey's data protection authority has fined WhatsApp nearly €200,000 for violating privacy rules.
The Facebook-owned messaging platform had "not clearly stated" how it would process its users' data and for what purpose.
WhatsApp has to take "the necessary measures to avoid processing personal data contrary to the law", the Turkish Personal Data Protection Authority (KVKK) said.
The sanction comes just one day after WhatsApp was fined a record €225m by Ireland's data privacy watchdog for breaking strict EU regulations.
Facebook has also been fined by Russian authorities for failing to store WhatsApp users' data on local servers.
WhatsApp came under fire in January after it asked its users to allow the app to share more data with Facebook.
The Turkish authority said it had sanctioned WhatsApp because it no longer offered users "free will".
"Users are obliged to give their consent to the contract as a whole," the authority said in a statement.
Euronews has contacted WhatsApp for a statement on the fine.
In January, Turkish authorities urged citizens to use a local messaging application, BiP, developed by mobile phone operator Turkcell, instead of WhatsApp.
Several Turkish institutions announced they had begun using BiP to communicate with journalists. Rival messaging apps Signal and Telegram have also seen a sudden increase in demand in Turkey.
The Head of Turkey's Digital Transformation Office has said that foreign applications pose serious security risks to Ankara.