Britain's data privacy regulator said on Thursday it was investigating 30 organisations including Facebook over their use of personal data and analytics in political campaigning.
The announcement came after Facebook admitted the personal data of up to 87 million users, mainly in the United States, was improperly shared with UK political consultancy Cambridge Analytica.
Information Commissioner Elizabeth Denham said in a statement she was "investigating 30 organisations, including Facebook".
"The ICO is looking at how data was collected from a third-party app on Facebook and shared with Cambridge Analytica.
"We are also conducting a broader investigation into how social media platforms were used in political campaigning," she said.
Denham said Facebook had been co-operating with the investigation and she was "pleased" with changes they have made.
But she added that "it is too early to say whether they are sufficient under the law," warning that the investigation "could result in enforcement action" and "policy recommendations".
Facebook has been scrambling for weeks in the face of the disclosures on hijacking of private data by the consulting group working for Donald Trump's 2016 campaign.
The British firm responded to the Facebook announcement by repeating its claim that it did not use data from the social network in the 2016 election.