San Francisco, Nov 17 (IANS): Facebook investors have increased pressure on Chairman and CEO Mark Zuckerberg to step down after a New York Times investigation suggested that the social network hired a Republican-owned political consulting and PR firm that "dug up dirt on its competitors".

According to a report in The Guardian on Saturday, Jonas Kron, Senior Vice President at Trillium Asset Management which owns a substantial stake in Facebook, "called on Zuckerberg to step down as board chairman in the wake of the report".

"Facebook is behaving like it's a special snowflake. It's not. It is a company and companies need to have a separation of chair and CEO," Kron was quoted as saying.

The New York Times report suggested that Facebook hired Definers Public Affairs, a Washington, D.C.-based conservative firm which did PR work for the social networking giant "and dug up dirt on the company's competitors and its critics".

In a press call, Zuckerberg denied he had any prior knowledge about this firm.

"After reading the article, I got on the phone with our team and we are no longer working with this firm," he said.

Definers allegedly "encouraged the depiction of Facebook's critics as anti-Semites and had published news articles criticising Facebook's competitors".

Another Facebook investor Natasha Lamb from Arjuna Capital said the combined role of chairman and chief executive means that "Facebook can avoid properly fixing problems inside the company", said the report.

According to TechCrunch, founded by a Republican campaign manager known for his dirt-digging prowess, Definers is far from a normal, politically neutral contractor.

In a statement, Facebook COO Sheryl Sandberg also denied any knowledge of the firm.

Facebook said that it used the consultant Definers Public Affairs to look into the funding of "Freedom from Facebook" to demonstrate that it was not simply a spontaneous grassroots campaign, as it claimed, "but supported by a well-known critic of our company," presumably liberal financier George Soros.

"To suggest that this was an anti-Semitic attack is reprehensible and untrue," the company added.

Facebook has also refuted allegation that it knew about Russian activity as early as the spring of 2016 but was slow to investigate it at every turn.

As fallout of the report, Facebook stocks fell 3 per cent on Friday to $139.53, the lowest since April 2017.