In the escalating battle over whether Herbalife is a legitimate business or a scam, the embattled company has found a vigorous champion in billionaire Carl Icahn, the activist investor who revealed in a securities filing earlier this month that he has taken a 13 percent stake in the vitamin and supplement maker. On Friday, Icahn continued his offensive against Herbalife’s detractors, taking aim at Sullivan & Cromwell in the process.

Appearing on CNBC’s Fast Money: Halftime Report, Carl Icahn repeatedly challenged S&C—which is among the law firms representing hedge fund titan William Ackman in his campaign to wipe out a company he claims is a pyramid scheme—to say publicly whether it shares the Pershing Square Capital Management CEO’s opinion that the vitamin and supplement maker is an elaborately constructed fraud.

Citing Ackman’s comments at the Harbor Investment Conference on Wednesday in New York, which The Wall Street Journal covered live, Icahn said, "He says Sullivan & Cromwell is comfortable that HLF is a pyramid scheme." (The Journal also reported that Ackman said at the conference that he had worked with S&C to support his claim that Herbalife is a scam.)

The comments come on the heels of the 342-slide report Ackman released in December that laid out why he believes the government should shut Herbalife down. S&C is referenced in a single footnote of the presentation as the source of information on Herbalife’s scant patent portfolio.

During his CNBC appearance, Icahn said he has trouble believing that S&C has embraced Ackman’s stance, or at least would do publicly. "I’m a betting man," he said on the program. "And I would bet and give odds that Sullivan & Cromwell has never said that publicly." He continued: "I challenge Ackman, who keeps talking about transparency, to bring out Sullivan & Cromwell and have a Sullivan & Cromwell attorney say that this is a pyramid scheme."

Icahn said Friday that his own lawyer, whom he described as having worked on Federal Trade Commission matters for 22 years, had issued an opinion that “Herbalife is a well-run legal multilevel marketing company." He added: "Now that means a lot.” (Icahn did not identify the lawyer.) Later in the program, Icahn took aim at S&C’s credentials, saying that while it is "a fine firm," it doesn’t have lawyers with enough experience dealing with the FTC’s Bureau of Consumer Protection to adequately advise on the Herbalife matter. CNBC has a full transcript of the Icahn interview posted on its website.

An S&C spokesman and two of the firm’s lawyers did not immediately respond to requests for comment Friday.

The Am Law Daily previously covered the Herbalife feud and the lawyers representing the various warring faction in January. At the time only Kirkland & Ellis had been identified as representing Ackman. Boies, Schiller & Flexner, meanwhile, has been called in to defend Los Angeles–based Herbalife and its CEO Michael Johnson.