Weight Loss Company Herbalife: The U.S. FBI is investigating Herbalife Ltd, the nutrition and weight loss company that hedge fund manager William Ackman has called a pyramid scheme, sources familiar with the investigation said on Friday based on the report from Reuters.

According to the same report, one source briefed on the matter said that the investigation has been going on for some time, but declined to give further details. A spokesman for the Federal Bureau of Investigation in Boston declined to confirm or deny the investigation. So far no charges have been filed in the matter.

According to Reuters, two other sources familiar with the matter said, "FBI agents are also studying Herbalife documents obtained from previous distributors."

The company has not received any inquiries from the FBI or the Justice Department about any investigation. But it would not be unusual for law enforcement to investigate a company without telling executives about it, Herbalife said on Friday.

The company has consistently denied running a pyramid scheme. Distributors earn more money for recruiting new members into the scheme than they do by selling products to consumers, pyramid scheme as defined.

Herbalife said in a statement, "We have no knowledge of any ongoing investigation by the DOJ (Department of Justice) or the FBI, and we have not received any formal nor informal request for information from either agency."

"News of the FBI probe comes roughly a month after Herbalife confirmed that the Federal Trade Commission had issued a civil investigative demand to the company to look more closely at how it works. In January, U.S. Senator Edward Markey called on the FTC and the Securities and Exchange Commission to investigate the company, in part because of allegations from civil rights groups that Herbalife unfairly targets minorities. Herbalife denies this.

The company, which reported sales of $4.8 billion last year, employs a vast network of independent distributors who sell its powders and shakes in more than 80 countries, including China, the company's fastest growing market," quoted from Reuters.

According to Yahoo News, the Federal Trade Commission says it has launched a civil inquiry into Herbalife, and the company has revealed that it also is being investigated by the Securities and Exchange Commission.