Speaking at a meeting of the Council of Institutional Investors' in Washington, Ackman said again that Herbalife has caused "enormous harm to a very vulnerable population" by targeting undocumented Latinos in the United States and other poor people.

Sparking some laughter in the audience, he urged everyone who might own stock in the company to sell it.

The company has vehemently denied running a pyramid scheme ever since Ackman's $20 billion hedge fund, Pershing Square Capital Management, first unveiled a $1 billion short bet against the company in December 2012. Federal and state regulators, including the Securities and Exchange Commission and the Federal Trade Commission, are investigating the company.

A spokeswoman for Herbalife said the company planned to respond shortly to Ackman's latest attack.

Ackman said that when he first bet against Herbalife, he had not anticipated that another billionaire investor, Carl Icahn, would come in, take a long view on the company and "go on CNBC once a week saying how great the company was and how bad I was."

Had Icahn not shown up, Ackman said, the whole thing would be over in a few months and Herbalife's alleged pyramid scheme would have collapsed.

He said he knows the SEC has limited resources to investigate wrongdoing and that the agency should have a "quarterly sit-downs" with the market's top short sellers to help detect fraud.

On the sidelines of Monday's conference, Ackman declined to discuss any meetings he may have had with regulators at the SEC or the FTC, but he acknowledged that he is meeting with some government officials while in Washington.

Herbalife's stock closed at $42.72 on Monday, up 13.47 percent for the year.

Pershing Square has felt the impact of Herbalife's recent stock climb, but the fund remains in the black with a gain of 4.6 percent for the year through March 24.