Pershing Square's Ackman: Why I think Herbalife is going to collapse

Bill Ackman, head of hedge fund Pershing Square Capital Management, said his firm's presentation of a Herbalife investigation will "expose incredible fraud."

The talk will be held at the AXA Equitable Center in Manhattan at 10 a.m. ET on Tuesday.

"We have hundreds of hours of internal video, Ackman told CNBC's Halftime Report. "We have some internal documents that were given to us by some employees."

"This will be the most important presentation that I have made in my career," he said. "We won't disappoint."

The hedge fund manager also invited Herbalife CEO Michael Johnson to attend the talk and "sit in the front row."

"The company is clearly panicking," Ackman said of Herbalife's recent Twitter campaign that called him the "Worst of Wall Street."

"These so-called nutritional clubs—places where people get together to talk about losing weight—that's not what's happening at these venues," he said.

Herbalife stock was down more than 6 percent after the interview.

"Herbalife is a company about great products and great company," said CFO John DeSimone in a statement. "We are proud of the tireless efforts of our millions of members around the world and know that their passion is what makes Herbalife the incredible company it is today."

DeSimone will be on CNBC at 9 a.m. ET on Tuesday.

Bill Ackman

Adam Jeffery | CNBC

Pershing Square is short on Herbalife and has climbed more than 25 percent during the first half of 2014 despite a rise in Herbalife's share price.

Last week, Ackman said he would love for activist investor Carl Icahn to sell his 17 million shares in Herbalife.

Read MoreGuess who brohugged? Yep. Ackman, Icahn

"That would be a great outcome for Carl, and that would be wonderful for us," Ackman said at the Delivering Alpha conference presented by CNBC and Institutional Investor.

Pharma deal ahead?

Ackman also said on Monday that the likelihood of Valeant Pharmaceuticals succeeding in its hostile takeover for Allergan increased after the Botox maker reported positive second-quarter results.

Read MoreAllergan posts profit, plans to cut 13% of workforce

"As the deal spread narrows, people perceive the probability [of the deal] increasing," said Ackman, whose firm holds a nearly 10 percent stake in Allergan.

The spread on the deal—or the difference between the value of the two companies' shares and the ratio implied by the deal's terms—had dropped more than 50 basis points to below 3 percent on Monday.

"The quality of those earnings is not very high quality," the hedge fund manager said. "The growth in earnings that you're seeing here is not driven by an increase in revenue growth."

"Really what they're doing is cutting out fat they really could have cut out a long time ago," he told CNBC.

Ackman's Pershing Square and Valeant made a joint offer for Allergan in April, which the company has rejected. The fund will not raise its bid, Ackman said.

Read MoreValeant complains to regulators about Allergan

—By CNBC.com. Reuters contributed to this report.