Attorney General Karl Racine is seeking internal documents that show how the social media giant penalizes users who violate its misinformation policies around vaccines, as well as materials related to a Facebook study about vaccine hesitancy among users, according to a copy of a subpoena issued by Racine’s office last month. The subpoena also demanded data on the total volume of content that has been removed or demoted by Facebook for violating its vaccine misinformation policies.

“Facebook has said it’s taking action to address the proliferation of Covid-19 vaccine misinformation on its site. But then when pressed to show its work, Facebook refused,” a spokeswoman for the attorney general said in a statement. “AG Racine’s investigation aims to make sure Facebook is truly taking all steps possible to minimize vaccine misinformation on its site and support public health.”

In a statement, Facebook said it’s removed more than 18 million pieces of content on Facebook and Instagram that violate its Covid-19 and vaccine misinformation policies, and labeled more than 167 million pieces of Covid-19 content that were rated false by its fact-checking network.

“We remain the only company to partner with more than 80 fact-checking organizations covering over 60 languages, using AI to scale those fact-checks against duplicate posts across our platform,” the company said. “We have consistently provided updates on our blog about our efforts to combat Covid-19 misinformation.”

The subpoena was reported earlier by Axios.

The spread of misinformation about Covid-19 vaccines has become a significant topic of discussion in Congress over the last few months. Democrats have pushed the tech giants to do more to eliminate conspiracy theories about the vaccines, which have proliferated over the course of the pandemic.