Billionaire Carl Icahn is extending a years-long proxy fight with fellow 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.

Shares of Herbalife, which have more than doubled since Ackman’s initial attack, were down 2 percent Friday.

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