Icahn takes an even larger stake in Herbalife

NEW YORK (AP) - Billionaire Carl Icahn is extending a years-long proxy fight with co-billionaire Bill Ackman, upping his stake in Herbalife yet again.

The two have been battling over the legitimacy of the supplements and weight loss company since 2012, when Ackman called Herbalife a pyramid scheme and revealed a massive bet against it.

A regulatory filing this week shows that Icahn upped the stakes again, pushing his ownership from 20.8 percent, up to 23.1 percent. He's the California company's biggest stakeholder. At $54.70 per share, Icahn put another $100 million plus into Herbalife on Thursday.

Shares of Herbalife, which have more than doubled since Ackman's initial attack, fell 3 percent Friday.

In July, The U.S. Federal Trade Commission closed its investigation of the company without labeling it a pyramid scheme, though its description of the business model was essentially that of a pyramid scheme.

The agency said Herbalife needs to rework the way in which it pays its salespeople. The FTC ruled that salespeople have to be paid for selling Herbalife products. Typically, Herbalife salespeople bought products and tried to get others to do the same.

Herbalife announced this week that CEO Michael Johnson will step down next year and be replaced by Chief Operating Officer Richard Goudis.