A court in California has alleged that Facebook used its apps to gather important data about users and their friends, including some who had not even signed up to the social network.
In a lawsuit brought by a former tech startup company Facebook is accused of reading their text messages, tracking locations and accessing people's photos on their phones.
Essentially the claims amount to mass surveillance. Facebook denies the claims.
The social media company has come under increasing pressure over alleged misuse of data.
Earlier this week CEO Mark Zuckerberg was questioned by European lawmakers who accused him of not offering enough assurances about the company's ability to protect users' private data.
Zuckerberg's appearance in Brussels cames three days before tough new EU rules on data protection were due to take effect. Companies will be subject to fines of up to 4 percent of global turnover for breaching them.