New York City begins a new era in nutritional warnings this week, when chain restaurants will have to start putting a special symbol on highly salty dishes.

The first-of-its-kind rule takes effect Tuesday. It will require a salt-shaker emblem on some sandwiches, salads and other menu items that top the recommended daily limit of 2,300 milligrams - about a teaspoon - of sodium.

It's the latest in a series of novel nutritional moves by the nation's biggest city, and it comes as health advocates, federal regulators and some in the food industry are trying to get Americans to cut down on salt. Experts say most Americans consume too much of it, raising their risks of high blood pressure and heart problems.

"With the high sodium warning label, New Yorkers will have easily accessible information that can affect their health," city Health Commissioner Dr. Mary Bassett said when the Board of Health approved the new warning in September. She's due to discuss it further at a news conference on Monday.

The average American consumes about 3,400 mg of salt per day, and public health advocates have cheered the measure as a smart step to make diners aware of how much sodium they're ordering. A T.G.I. Friday's New York cheddar and bacon burger counts 4,280 mg, for example; a Chili's boneless Buffalo chicken salad has 3,460 mg. The figures come from the companies' published nutritional information.

But salt producers say the city is acting on misimpressions about the risks of salt in New Yorkers' diets. An international study involving 100,000 people suggested last year that most people's salt intake was OK for heart health, though other scientists faulted the study.

Restaurateurs say that healthy-eating initiatives shouldn't single out any one ingredient and that the city shouldn't create its own salt-warning scheme when federal regulators are working on new, national sodium guidelines.

"Every one of these cumbersome new laws makes it tougher and tougher for restaurants to find success," New York State Restaurant Association President Melissa Fleischut said when the city health board approved the salt requirement.

It will apply to an estimated 10 percent of menu items at the New York City outlets of chains with at least 15 outlets nationwide, according to the Health Department. Officials say those chains do about one-third of the city's restaurant business.

While eateries are expected to comply as of Tuesday, the city won't start collecting fines until March 1.

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In recent years, New York City has pioneered banning trans fats from restaurant meals and forcing chain eateries to post calorie counts on menus. It led development of voluntary salt-reduction targets for various table staples and tried, unsuccessfully, to limit the size of some sugary drinks.