NEW YORK – A feud between Wall Street titans is flaring up again over Herbalife.

Carl Icahn has taken a 13 percent stake in the supplement company that Pershing Square Capital Management's William Ackman calls a pyramid scheme. Ackman has bet that the company's stock price will fall.

Icahn's investment, revealed in a filing with the Securities and Exchange Commission late Thursday, comes three weeks after a spat between the two men boiled over on live television, with each phoning in to CNBC and insulting each other.