PepsiCo Inc. (PEP) and two other energy- drink makers are being investigated by the New York attorney general over their marketing practices, according to a person familiar with the probe.

Attorney General Eric Schneiderman in July subpoenaed PepsiCo, maker of the Amp energy drink, as well as Monster Beverage Corp. (MNST) and Living Essentials LLC, which makes 5-Hour Energy, said the person, who declined to be named because the person wasn’t authorized to speak publicly about the probe.

Schneiderman’s office is investigating the companies’ marketing practices and ingredient disclosures, including whether energy drinks are improperly marketed as dietary supplements, the person said. The companies also don’t disclose the true amount of caffeine in the drinks, the person said.

The probe is in its early stages and could broaden, the person said.

Michelle Duffy, a spokeswoman for Schneiderman, declined to comment. The probe was reported earlier by the Wall Street Journal.

Monster, the largest U.S. energy-drink maker by volume sales, said in a regulatory filing this month that an unspecified attorney general was investigating the company’s flagship drink and ingredients.

Roger Pondel, a spokesman for Corona, California-based Monster, declined to comment. Jeff Dahncke, a spokesman for Purchase, New York-based PepsiCo, also declined to comment.

Elaine Lutz, a spokeswoman for 5-hour Energy, said the company had no additional comment beyond an earlier bond offering filing.

“We will appropriately disclose any new, material information,” Lutz said today in an e-mail.

To contact the reporter on this story: David McLaughlin in New York at dmclaughlin9@bloomberg.net

To contact the editor responsible for this story: John Pickering at jpickering@bloomberg.net