NEW YORK — An investigation of the herbal supplements industry by New York’s attorney general has now expanded into a multistate probe.

New York Attorney General Eric Schneiderman on Tuesday announced the formation of a coalition of state attorneys general from Connecticut, Indiana and Puerto Rico to further investigate the herbal supplement industry business practices.

The effort aims to foster transparency to ensure that supplement makers are taking steps needed to validate their marketing claims, including authenticity and purity, the New York attorney general’s office said.

“I am pleased to announce this historic partnership to protect the millions of people who buy herbal supplements from potentially false and misleading business practices,” Schneiderman said. “New Yorkers and consumers nationwide deserve confidence that when an herbal supplement is represented as authentic, pure and natural, it really is.”

The New York investigation was announced in early February, when Schneiderman’s office sent cease-and-desist letters to Walgreens, Walmart, Target and GNC to stop selling certain store-brand herbal supplements because DNA barcode testing couldn’t verify that the products contained the labeled substance, or the supplements were found to contain ingredients not listed on the labels.

The store brands at issue were GNC’s Herbal Plus, Walgreens’ Finest Nutrition, Walmart’s Spring Valley and Target’s Up & Up. Tested supplement products included gingko biloba, St. John’s wort, ginseng, garlic, echinacea and saw palmetto.

Then in late February, Schneiderman’s office expanded its probe by sending letters to four manufacturers of dietary supplements — Pharmavite LLC, Nature’s Way Products Inc., NBTY Inc. and Nutraceutical Corp. — to request information on the ingredients and quality control measures used for their products sold in New York.

“Clearly, the questions we raised about the herbal supplements sold in New York resonate outside of our borders,” Schneiderman said Tuesday about the multistate coalition. “By joining together, and building on the long track record of state attorneys general upholding the rights of consumers, we can go further in investigating this industry and, as needed, in achieving reform. I look forward to collaborating with these partners on this vital work.”

The New York attorney general reported that an estimated 65,000 dietary supplements are now on the market and are consumed by more than 150 million Americans, according to 2013 study from the Canadian Institutes of Health Research. His office also said the Natural Products Foundation estimated that the dietary supplement industry contributes $61 billion dollars to the U.S. economy.

“Consumers are entitled to expect that the product they are purchasing actually contains the ingredients as listed on the label,” Connecticut Attorney General George Jepsen said. “The findings uncovered by Attorney General Schneiderman raise serious public health and consumer protection concerns, potentially impacting consumers in Connecticut and across the country.”

The attorneys general noted that although the U.S. Food and Drug Administration requires companies to verify that their products are safe and correctly labeled for their contents, dietary supplements don’t undergo the FDA’s rigorous evaluation process for drugs, which runs from the design of clinical trials to the severity of side effects to the conditions in which a product is manufactured. Schneiderman’s office reported that more than half of FDA Class I drug recalls between 2004 and 2012 were for “dietary supplements.”

“The significant issues recently raised about herbal supplements are a concern that must be taken seriously so as not to further jeopardize the health and safety of people ingesting these products,” said Indiana Attorney General Greg Zoeller. “As state consumer protection advocates, my fellow attorneys general and I are focused on efforts to eliminate misleading and deceptive labeling for the benefit of consumers.”

Stakeholders in the supplement industry have criticized the New York investigation, saying supplement makers adhere to strict manufacturing and quality control standards. In particular, they blasted the investigation’s reliance on DNA barcode testing, which they called an unreliable and limited method for testing the identity of herbal dietary supplements.

“The New York attorney general’s office continues to ignore the scientific facts of his investigation, as well as the fact that botanical supplements are already properly regulated by the Food and Drug Administration,” Steve Mister, president and chief executive officer of the Council for Responsible Nutrition (CRN), said on Tuesday. “It’s ironic that he continues to call for transparency, when his office refuses to release its test results and methodology, which scientists familiar with botanicals and DNA testing say is inaccurate. It’s unfortunate that he has pulled other states into this misguided effort, because clearly these supplements are products that consumers find beneficial. There’s no safety issue that warrants this high-level investigation and misuse of tax payers money.”

Also on Tuesday, GNC Holdings Inc. said that independent, third-party testing of certain product lots in GNC’s Herbal Plus supplements line confirmed that the products meet all regulatory requirements for safety, quality, purity and proper labeling.

“This additional round of tests leaves no doubt that our products are not only pure but are in full compliance with all regulatory requirements,” said Michael Archbold, CEO of GNC. “When generally and widely accepted industry tests sanctioned by the global governing bodies that set standards for product purity and quality are used, GNC products are fully compliant. We share the attorney general’s objective of ensuring that consumers can rely on companies like GNC to deliver pure, properly labeled products and, as expected, these results demonstrate that fact.”

Recently, the Natural Products Association (NPA) announced that it has partnered with quality assurance company UL Verification Services Inc. to certify that dietary supplement makers are following federal guidelines and regulations, including Good Manufacturing Practices (GMP).

NPA said that the association and UL have developed a co-branded, supplement-specific badge logo program for use in product labeling and marketing materials, including websites and social media, for dietary supplements. The use of both the NPA and UL marks in its co-branded partnership will only be available for companies certified under the NPA GMP standard, with audits conducted by UL.

“This new certification partnership will leverage UL’s rich history of quality and safety and NPA’s industry-first standard to transform the industry and bring it into a new world of best practices,” NPA executive director and CEO Daniel Fabricant commented when the partnership was announced. “This has been in the works for some time, but it is especially timely today because consumers should have confidence that their vitamins and supplements are safe and high quality.”