Facebook faces a new controversy over alleged tactics it used to discredit its critics, embarrass rival firms and downplay problems at the company.
The New York Times has published a wide-ranging account of the methods Facebook and a public relations firm used to “deny and deflect” criticism.
The report has led US lawmakers to call for tighter regulation of social networks.
Facebook has denied several of the claims.
The newspaper said PR firm Definers had circulated a document suggesting Mr Soros was the hidden backer of anti-Facebook movement Freedom from Facebook.
The document encouraged journalists to explore the financial connections between anti-Facebook groups and Mr Soros, who is frequently the target of conspiracy theories and anti-Semitic smears.
Mr Soros’s Open Society Foundations said it had not made any grants to support campaigns against Facebook. It said Facebook’s behaviour was “astonishing”.
“Your methods threaten the very values underpinning our democracy,” said its president, Patrick Gaspard.
Responding to the article, Facebook said it had wanted to show that Freedom From Facebook was “not simply a spontaneous grassroots campaign” and that the movement was “supported by a well-known critic of our company”.
It said any suggestion that it had been an anti-Semitic attack was “reprehensible”.