A Belgian court has threatened Facebook with a fine of up to 100 million euros ($156 million) if it continued to break privacy laws by tracking people on third-party websites.
In a case brought by Belgium's privacy watchdog, the court also ruled that Facebook had to delete all data it had gathered illegally on Belgian citizens, including people who were not Facebook users.
Facebook, which will be fined 250,000 euros ($392,000) a day or up to 100 million euros if it does not comply with the court's judgement, said in a statement it would appeal the ruling.
"Facebook informs us insufficiently about gathering information about us, the kind of data it collects, what it does with that data and how long it stores it," the court said in a statement.
"It also does not gain our consent to collect and store all this information."
The social media giant uses different methods to track the online behaviour of people if they are not on the company's website by placing cookies and invisible pixels on third-party websites, the court said.
Facebook said the technologies it uses were in line with industry standards and it gives users the right to opt out of data collection on websites and applications off its platform being used for advertisements.
"We'll comply with this new law, just as we've complied with existing data protection law in Europe," Facebook's vice-president of public policy for Europe Richard Allan said.
Belgium's privacy watchdog welcomed the ruling.
"Facebook has just launched a large campaign where they stress the importance of privacy," it said.
"We hope they will now make this a reality".