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Ackman accuses Herbalife of being a pyramid scheme but he has not spoken at length about the company since the December 2012 announcement of his short position, which has cost his $12 billion Pershing Square Capital Management hundreds of millions in unrealized losses.
He plans to present his case a second time - likely with hundreds of power-point slides being prepared by a team of analysts - at the Robin Hood Investments Conference in New York, the source said, requesting anonymity as they were not authorized to speak publicly.
The gathering is the first investor conference sponsored by the hedge fund industry's anti-poverty charity, and managers have been asked to keep their ideas secret until they take the stage because attendees pay thousands of dollars to hear their new ideas first.
On Thursday, Daniel Loeb revealed a $1 billion stake in Japan's SoftBank and David Einhorn disclosed a stake in chipmaker Micron Technology.
Herbalife has repeatedly denied that it is a pyramid scheme, which typically tries to make money by recruiting new members who pay fees rather than relying only on the sale of goods.
But Ackman says the company's share price will eventually fall to zero once regulators step in.
The share price fell 2.59 percent on Thursday but is still up 107 percent for the year, making other prominent investors including Carl Icahn and Soros Fund Management rich.
Even so, there are new signs that regulators are keeping a close eye on multi-level marketing companies.
Last week Massachusetts' top securities regulator William Galvin shut down World Capital Markets, a multi-level marketing company which sold cloud services mainly to the Brazilian community. Galvin said people who paid thousands in fees are still owed $100,000 in unpaid compensation.
In October the Securities and Exchange Commission shut down CKB, a company that sold educational products and largely targeted the Asian-American community, for having had "little or no real-world retail sales."
Also in October, a federal judge said the company will have to defend itself against allegations from Dana Bostick, a former Herbalife distributor, that it is a "pyramid scheme."
This week Jim Chanos, who runs Kynikos Associates and had also had a short bet on Herbalife late last year, said at the Reuters Investment Outlook Summit that retail sales at Herbalife have long been debated by a number of investors.
(Editing by Stephen Coates)
By Svea Herbst-Bayliss
