A report that both the U.S. Department of Justice and the FBI are investigating Herbalife sent shares of the nutritional supplement company sliding 14 percent on Friday.
A Financial Times story quoted sources that said the Manhattan offices of both agencies were looking into the downtown Los Angeles company's multilevel marketing practices, which have been under attack by hedge fund manager Bill Ackman for more than a year.
The company already is facing a civil inquiry from the Federal Trade Commission.
Herbalife said it was unaware of any criminal investigation.
"We have not received any formal or informal request for information from either agency," the company said in a statement.
Shares closed down $8.39 to $51.45 on the New York Stock Exchange.