A 16-ounce can of Hershey's Chocolate Milk Mix sells for $1.89 at a local supermarket. One shelf over, the same size can of Hershey's with a virtually identical label is for sale at the same price.

But look again: the second can contains 14.5 ounces -- 9 percent less than the first.

In food industry parlance, the Hershey's product has been "downsized." Like dozens of other packaged goods, from tuna fish to laundry detergent to spaghetti sauce, the net weight of the product has been reduced while its price and outer package remain identical or virtually the same.

Downsizing isn't new nor is it illegal. But some consumer groups and government agencies see the practice as deceptive and on the increase.

In recent months, Consumer Reports magazine said it has received hundreds of complaints from readers about products that have been downsized without a coinciding drop in price. Inspired by similar complaints, attorneys general in at least three states -- New York, Texas and California -- have begun examining manufacturers' packaging techniques for evidence of fraud.

In an investigation of New York and New Jersey supermarkets over the past two months, representatives of the New York state attorney general's office reported that the contents of 30 well-known products had been reduced without a change in price or packaging.

Investigators found, for example, that Quaker Oats Co. had reduced its beef-flavor Rice-A-Roni product to 6.9 ounces from 8 ounces but had not reduced the size of the package. A Quaker Oats spokesman, Ron Bottrell, said the company is considering a smaller package, but a change "is not something that can be done overnight." The reduced-size product was introduced last fall.

Some critics of the practice said the recession has increased the pressure on manufacturers to downsize brands.

"Any time the economy drops, we see across the spectrum of marketers an increased willingness to engage in deceptive activity," said Steve Gardner, assistant attorney general of Texas. "In this case, they aren't playing fair. The consumer is going to be tricked into buying something that doesn't exist."

According Gordon Hard of Consumer Reports, downsizing follows from a simple principal of consumer behavior: Price-conscious shoppers will stop buying a product if its price is increased, but they may not notice the difference if the contents are slightly reduced and the price is relatively unchanged.

"It's a pricing strategy that is dubious at best and at worst could backfire on the manufacturer," Hard said. "It breeds ill will when regular customers notice the deception."

New York State Attorney General Robert Abrams, who argues that downsizing amounts to a "hidden price increase" that costs consumers millions of dollars each year, said he will propose legislation in Albany next month requiring companies to disclose when they reduce the amount of content in a product but do not alter the packaging.

By downsizing a product, companies often realize substantial savings on ingredients without a significant loss of sales. General Foods will conserve millions of pounds of coffee this year -- the company declined to disclose precise amounts -- by packaging 11.5 ounces of Brim Dark Decaf Coffee in a can that once held 13 ounces. The reduction is a result of "puffing" technology that expands the volume of each coffee bean and increases its yield but does not compromise its quality, the company said.

Federal law requires manufacturers to disclose the net weight of their products, but no statutes require companies to signal to consumers when the content has been changed, according to the Federal Trade Commission and the Food and Drug Administration, which enforce product labeling regulations.

Although Abrams's proposal would cover products marketed only in New York, the legislation could influence labeling practices in all 50 states because of the difficulty national marketers would face in changing their labeling for just one state.

"If it's legal in 49 states and not in another, it poses a real problem," said Quaker Oats's Bottrell. "We feel those types of questions, and they are legitimate questions, need to be resolved at the federal level."

Abrams said consumers usually don't notice downsizing because supermarkets typically replace the older, weightier version of the product with the smaller version in short order, making side-by-side comparisons difficult. The packaging of the new product is identical or only slightly different, making it otherwise indistinguishable from the old one, he said.

Based on its investigation, the New York attorney general's staff said some of the nation's biggest food marketers recently downsized their products, including Hershey Foods Corp., Thomas J. Lipton Co., Quaker Oats Co., Gerber Products Co. and General Foods, a subsidiary of Philip Morris Co.

Marketers dispute the suggestion that downsizing a product constitutes deception. In fact, spokesmen for Campbell Soup Co. and Quaker Oats said that their market research indicates that consumers prefer a reduced amount of product to a price increase.

Representatives of Lipton, General Foods and Hershey said their products have been reprocessed in more concentrated form that produces the same results as the old product. These changes have reduced the products' weight but not their volume, meaning that it takes the same package to hold a lighter product.

For example, Hershey said its new 14.5-ounce chocolate mix has been formulated so consumers receive the same number of servings as they would from the 16-ounce version. "It's the same value to the consumer," said Bonnie Glass, a Hershey spokeswoman.

Yet consumers wouldn't know a difference from looking at the two cans. Although Hershey discloses that the new can contains 14.5 ounces, as required, it doesn't identify the product as "more concentrated" or "reformulated."

"The reasoning behind {not doing so} is that it really isn't different," said Glass. "We are producing it differently but the end result is the same."

Other companies said they change a product's content in response to changes in their cost of ingredients or in response to changes in the size of competitors' brands. Campbell's said it reduced the amount of its Prego spaghetti sauce but kept the price the same after rival Ragu moved first. "This is a very competitive business," said Marsha Cade of Campbell's. The reduction "gives Ragu more money to put into marketing. In order to be more competitive, we have to do the same."

Sometimes, marketers said, they put more product in a package without increasing the price and without getting credit for such moves. "We'd like to see the report on the products that have been up-weighted," said Larry Hicks, general counsel of Thomas J. Lipton Co.