The Wall Street Journal reports that the Federal Bureau of Investigation and federal prosecutors have conducted interviews and sent document requests to determine whether people — including some hired by Ackman — made false statements about the company’s business model to regulators and others in order to inspire investigations into the company.

Herbalife’s (HLF) stock has see-sawed for more than two years, beginning in late 2012 when Ackman initially called the company a pyramid scheme and disclosed he held an “enormous” short position in Herbalife’s stock. He has renewed attacks against the company periodically since his initial announcement, including a presentation last summer that he said would result in a “death blow.” Wall Street shrugged off Ackman’s statements at the time. Further attacks came as recently as January of this year, when Ackman said he expected Herbalife’s stock price to collapse to zero and said it would happen within a year.

Herbalife, which has been to this rodeo many times, issued a statement to address the reports of a criminal investigation into the campaign orchestrated by Ackman.

“Mr. Ackman has a $1 billion bet against Herbalife and a direct financial interest in hurting our company,” said Alan Hoffman, an executive vice president at Herbalife. “For more than two years, he has spent over $75 million orchestrating a false and fabricated attack against Herbalife, all in an effort to enrich himself.”

Appearing on CNBC Friday morning, Ackman said he had not been contacted by federal agencies.

Ackman confirmed that some people hired by Global Strategy Group, a consultancy working for Ackman’s Pershing Square Capital Management LP, had received subpoenas from the Department of Justice. The investor said he was not worried about the investigation leading back to him. Ackman also said he could not be certain if people working for Global Strategy Group had not made false statements.

A Pershing Square representative said the company had been “completely transparent about our position and our research, and we have acted lawfully in every respect.”

“We are proud of our work over the past two years exposing the pervasive victimization by Herbalife of millions of people and would welcome any scrutiny of those efforts,” the representative said.

Herbalife’s shares have swung wildly of late, dipping below $30 in late 2012 when Ackman first began to talk about the company but rallying to above $80 a year later. Shortly after Ackman’s initial short position, activist investor Carl Icahn also got involved, placing a bet against Ackman. The billionaires fought about Herbalife and other long-standing gripes in an epic argument that was televised by CNBC. Icahn remains the largest Herbalife shareholder, owning a little more than 18% of the company.

—Reuters contributed to this report.