On the same day that CEO Mark Zuckerberg is due to testify about issues related to the Cambridge Analytica scandal, the Associated Press revealed that a secret complaint had been filed with the Securities and Exchange Commission surrounding Facebook’s complicity in the illegal sales of animal parts.

According to the report, wildlife preservation advocates have claimed that Facebook runs ads on pages that are run by “overseas wildlife traffickers illegally selling the body parts of threatened animals,” including ivory and rhino horns. The social media giant’s failure to stop these traffickers from using the site as marketplace, they argue, violates its “responsibilities as a publicly traded company.”

The complaint may also be used to investigate whether or how much of Facebook’s advertising revenue has been acquired through the ads run on such pages. AP notes that Facebook has not previously disclosed in regulatory filings that its revenue could be tied to this illegal trafficking.

While wildlife monitoring and advocacy groups have accused the social media site of allowing the sale of protected and endangered species in the past, the subject has received renewed attention in recent weeks. Facebook joined dozens of other technology companies in a pledge to prevent such illegal trade, joining the Global Coalition to End Wildlife Trafficking Online in early March. Yet in the weeks since the announcement, investigators and reporters alike have found no noticeable changes, continuing to see illegal items being offered for sale on Facebook.

The SEC complaint was initially filed last August by the National Whistleblower Center on behalf of an undercover informant, reports the AP.