California Attorney General Xavier Becerra offered few details about the probe and said he was disclosing it only because his office was making a public court filing to force Facebook to answer subpoenas, to which he said Facebook had thus far failed to respond adequately.
According to the filing, Facebook took a year to fully respond to an initial June 2018 subpoena related to the scandal in which Cambridge Analytica obtained the data of more than 50 million Facebook users – and used that data to influence political outcomes in the US in 2016.
The attorney general then asked for more information, including communications among executives related to developers’ access to user data and privacy-related news stories.
The filing said that Facebook “broadly refuses to answer the interrogatories or comply with the subpoena”, adding that the company has refused to search the emails of top executives Mark Zuckerberg and Sheryl Sandberg in response to the second subpoena.
Facebook didn’t immediately respond to a request for comment.
The investigation is into Facebook’s practices related to privacy, disclosures and third-party access to user data.
The state is looking into whether Facebook violated California law by deceiving users and misrepresenting privacy practices.
Officials say the probe began in early 2018 as a response to the Cambridge Analytica scandal, but has since expanded.
The court filing says Facebook has not yet given answers for 19 of the attorney general’s questions, or provided any new documents in response to six document requests.
The filing says Facebook is dragging its feet and also simply not complying with subpoenas or responding to questions.
California did not join a separate probe involving attorneys general from New York and other US states. The New York probe is looking into Facebook’s dominance and any resulting anticompetitive conduct.
The US Federal Trade Commission recently fined Facebook $5bn over privacy violations, though the penalty was criticised by consumer advocates and a number of public officials as being too lenient.