The European Court of Justice (ECJ) ruled Monday that companies in the European Union that embed the Facebook "Like" button on their websites are to be held liable for collecting data. By clicking the "Like" button, users would be transferring their personal data to Facebook. 

"The operators of a website that features a Facebook 'Like' button can be a controller jointly with Facebook in respect of the collection and transmission to Facebook of the personal data of the visitors to its website," judges from the Luxembourg-based court said. 

Facebook said it is "carefully reviewing" the court's decision. 

The case landed in Luxembourg after clothing business Fashion ID was taken to court in Germany in 2015 by the German consumer protection association in North Rhine-Westphalia. 

Fashion ID had embedded a Facebook "Like" button on its website, which caused the consumer protection group to file a lawsuit to get the company to remove the button from its page. The case went through the German legal system before reaching Luxembourg.

In Europe, data privacy is a major issue, with the EU implementing the General Data Protection Regulation in May 2018, which forced controllers of personal data to implement certain measures to protect privacy. 

The European debate on data privacy is also influenced by historical factors. Germany views privacy as a sensitive issue due to the East German secret police, also known as the Stasi, which spied on citizens when the country was divided. The organization existed from 1950 to 1990 and had personal files on millions of Germans due to its mass surveillance practices.  

Facebook has come under scrutiny for its data privacy policies in the past. The company last week was forced by the U.S. Federal Trade Commission to pay $5 billion in compensation for undermining user privacy. 

In March 2018, it was revealed that political data firm Cambridge Analytica was using Facebook to collect data on millions of Americans. The scandal meant increased scrutiny into Facebook's privacy practices, with CEO and founder Mark Zuckerberg testifying weeks later in front of Congress.