The Food and Drug Administration in late February sent warning letters to 17 food manufacturers it said violated the Food, Drug and Cosmetic Act and related federal regulations by making false or misleading health or nutrient claims on product packaging and their web sites. Twenty-two food products were involved. The companies were directed to advise the F.D.A. within 15 days on how they will correct the labeling and come into compliance with federal regulations. The agency warned a failure to correct the violations might result in “regulatory action without further notice, such as seizure and/or injunction.”

The companies deemed in violation of federal regulations pertaining to product labeling were large, such as Nestle Nutrition and Beech-Nut, which manufacture, among other things, infant and toddler foods, and small, like POM Wonderful, a Los Angeles-based manufacturer of pomegranate juice.

On March 3, following the dispatch of the warning letters, Margaret Hamburg, F.D.A. commissioner, sent an open letter to the food industry explaining the action. Dr. Hamburg noted despite concerns expressed in a previous “dear industry” letter issued last October, “we continue to see products marketed with labeling that violates established labeling standards.”

Dr. Hamburg noted the following violations were committed by the offending companies.

Some companies used nutrient content claims on packaging of foods meant for children under the age of two years that the F.D.A. only authorized for use on foods for adults.

“Such claims are highly inappropriate when they appear on food for infants and toddlers because it is well known that the nutritional needs of the very young are different from those of adults,” Dr. Hamburg said.

Some products had front-of-package labels declaring they contained no trans fats, which implied the products were better choices than those without the claim. But, Dr. Hamburg said the “no trans fats” claim may be misleading when a product instead is high in saturated fat, “and especially so when the claim is not accompanied by the required statement referring consumers to the more complete information on the Nutrition Facts label.”

There were products, including green tea, pomegranate juice, olive oil and walnuts, that claimed to treat or mitigate diseases. Under federal law, products performing such functions are considered drugs and must meet the regulatory requirements for drugs, including the requirement to prove the product is safe and effective for the intended use, Dr. Hamburg said.

There were products with misleading “healthy” claims when the foods involved did not meet the established criteria for use of that term.

And there were juice product labels that misled consumers into believing the products consisted entirely of a single juice when, in fact, they did not.

“Despite numerous admonitions from F.D.A. over the years, we continue to see juice blends being inaccurately labeled as single-juice products,” Dr. Hamburg said.

Dr. Hamburg said the violations uncovered were not indicative of the labeling practices of the food industry as a whole.

“In my conversations with industry leaders, I sense a strong desire within the industry for a level playing

field and a commitment to producing safe, healthy products,” Dr. Hamburg said. “That reinforces my belief that F.D.A. should provide as clear and consistent guidance as possible about food labeling claims and nutrition information in general, and specifically about how the growing use of front-of-pack calorie and nutrient information can best help consumers constructing healthy diets.”

Dr. Hamburg said she hoped the warning letters would give food manufacturers further clarification of what is expected of them as they review their current labels.

Reactions to the warning letters from the companies that received them varied, but most indicated they were ready to cooperate with the F.D.A. Diamond Foods, which was cited by the F.D.A. for making claims its walnuts will treat, prevent or cure diseases such as heart disease, arthritis and cancer, said, “We expect to be able to make any changes required to our packaging and web site expeditiously and with minimal expense.”

Nestle, some of whose Gerber’s infant and toddler food products carried claims approved by the F.D.A. but only for adults, said it would fully cooperate with the agency “to bring this matter to a conclusion.”

The reaction from POM Wonderful seemed more defensive. The F.D.A. said POM Wonderful made claims its products, primarily pomegranate juice, would treat, prevent or cure diseases such as hypertension, diabetes and cancer. POM said in a notice on its web site, “As strong advocates of honest labeling and fair advertising, POM Wonderful wants its customers to know that all statements made in connection with our products are true and are supported by an unprecedented body of scientific research. POM is confident about the depth of our research; we look forward to working with the F.D.A. to resolve these issues and to continue clear and honest communications with consumers about the health benefits of our products.”