A group of 14 state attorneys general on Thursday asked the U.S. Congress to investigate the herbal supplements industry after a New York probe of the products turned up ingredients that were not listed on labels and raised safety concerns.

The group, led by New York Attorney General Eric Schneiderman and Illinois Attorney General Greg Zoeller, also asked Congress to consider giving the U.S. Food and Drug Administration more oversight of herbal supplements.

“We believe the safety and efficacy of these supplements is a matter of deep public concern across the country,” the attorneys general said in the letter, urging “swift action.”

In February, four major retailers, GNC Holdings Inc, Target Corp, Walgreens and Wal Mart Stores Inc , halted sales of certain supplements after being subpoenaed by the New York attorney general. DNA tests had failed to detect plant materials listed on the majority of products tested.

On Monday, GNC reached an agreement with Schneiderman to adopt more stringent testing standards than the FDA requires, and began to resell the supplements.

A study found the products were within FDA guidelines, Schneiderman said. GNC said tests also showed its products were safe, pure, properly labeled and in full compliance.

The attorneys general sent their letter requesting a probe to Kansas Senator Jerry Moran and Pennsylvania Representative Joe Pitts, chairmen of subcommittees on product safety and health. They cited the New York probe and said researchers also have found other problems, including high levels of lead, mercury and arsenic in certain supplements.

The letter was signed by attorneys general from Connecticut, District of Columbia, Hawaii, Idaho, Indiana, Iowa, Kentucky, Massachusetts, Mississippi, New Hampshire, New York, Northern Mariana Islands, Pennsylvania and Rhode Island.

The attorneys general asked the subcommittees to work with the FDA to see whether the agency should develop enhanced quality assurance programs and other safety requirements. Currently, the FDA regulates dietary supplements under a different set of rules than those covering drug products.

Steve Mister, president of the Council for Responsible Nutrition, an industry group, said the New York attorney general’s investigation was discredited and concerns about “alleged widespread safety issues are not true.”

He said “the industry is already amply regulated on a federal level.”

(Reporting By Karen Freifeld; Editing by David Gregorio)