Herbalife Ltd. (NYSE:HLF) is going to face yet another big attack from billionaire hedge fund manager Bill Ackman later this week.Short interest in the stock has grown to more than 13% of the float in the past few weeks as federal and state authorities opened investigations into the company’s business practices. Herbalife shares have declined more than 25% this year.

Bill Ackman Herbalife

Ackman’s another attempt to prove that Herbalife is a pyramid scheme

Bill Ackman has decided to publicly showcase a documentary about Herbalife Ltd. (NYSE:HLF)’s former distributors who say that the company defrauded them. Ackman has shorted Herbalife stock since May 1, 2012. His hedge fund Pershing Square Capital Management is betting $1 billion that the stock would collapse because Herbalife is a pyramid scheme. However, shares of the nutritional supplement maker soared more than 165% in 2013 as Dan Loeb and Carl Icahn took bullish positions in the company.

The documentary will be Ackman’s latest evidence that the Cayman Islands-based company is a pyramid scheme, reports The New York Post. Pershing Square has planned an event in the New York City this Friday to showcase the documentary. The hedge fund has invited members of the community, government, press and consumer organizations to attend the showing. Ackman didn’t reveal the exact time and place to prevent any interference at the event.

The documentary will be followed by a live panel discussion with former Herbalife Ltd. (NYSE:HLF) distributors featured in the film. The discussion will be moderated by Connie Chung, the former CBS News anchor. Chung said she would not accept payments for the gig. Pershing Square said it hasn’t compensated people in the documentary beyond expenses for people coming to New York.

Herbalife launches attack on Ackman

Meanwhile, Herbalife Ltd. (NYSE:HLF) attacked Ackman last week after the hedge fund manager acknowledged that he agreed to pay a former Herbalife executive to become a whistleblower against the company. According to ABC News, Ackman had offered to pay $3.6 million to a former employee of the nutritional supplement maker over the next 10 years for when he lost his job after revealing information about the company to the media and federal investigators.

Herbalife Ltd. (NYSE:HLF) alleged that these payments were part of Ackman’s larger effort to offer secret payments to organizations and people to bring misleading and false charges against the company.

Herbalife Ltd. (NYSE:HLF) shares soared 2.01% to $58.99 in pre-market trading Monday.