Facebook said its No. 2 executive, Sheryl Sandberg, asked staff to investigate whether billionaire philanthropist George Soros, in calling the company a "menace," had financial motivations against it.
This revelation follows prior disclosures that the company had done opposition research on him.
Friday's statement from Facebook is in response to a New York Times article that describes Sandberg asking Facebook staff to look into Soros' financial interests in speaking out against the company. Soros called Facebook a "menace to society" in a January speech.
Facebook said the company was already researching Soros when Sandberg sent an email asking if Soros had shorted Facebook stock. Shorting a stock is essentially taking a bet it will decline.
Soros's Open Society Foundations did not immediately respond to a request for comment on Friday.
In a Thanksgiving eve post, outgoing executive Elliot Schrage took the blame for hiring the public relations firm doing opposition research on critics.
Schrage has been at Facebook for a decade and announced his departure in June. In the post, he acknowledges that Facebook asked the firm, Definers, "to do work" on Soros. Definers also helped respond to what Schrage described as unfair claims about the company.
Sandberg followed Schrage's note of contrition with one of her own, acknowledging her responsibility for overseeing Facebook's communications team. On Definers, Sandberg said "some of their work was incorporated into materials presented to me and I received a small number of emails where Definers was referenced."