New York City begins a new era in nutritional warnings on Tuesday by requiring many chain restaurants to post a warning label on menu items that have high sodium content.

The rule – believed to be the first of its kind in the country – requires that an emblem of a saltshaker encased in a black triangle be placed next to any menu item that contains more than 2,300 milligrams of sodium, roughly equivalent to 1 teaspoon of salt.

The rule applies toward any restaurant chain with 15 or more locations nationwide and requires the establishments to post a warning statement where customers place their orders.

Chains have until March 1 to comply with the new rule before the possibility of receiving a fine.

“The American Heart Association is thrilled for the pending implementation of the Sodium Warning Label rule,” said Robin Vitale, senior director of government relations for the American Heart Association. “Americans are consuming dangerous levels of sodium, most often found in processed or restaurant food. This rule will help to increase transparency.”

The warning label rule, which passed unanimously in September, does not limit how much sodium can be in food and does not penalize restaurants that serve food with more than the recommended daily amount. Instead, it is meant to help consumers understand and identify the sodium levels in their food choices.

The move comes as health advocates, federal regulators and some in the food industry try to educate Americans about the dangers of too much salt.  Increased sodium intake leads to elevated blood pressure, which is a leading risk factor for strokes and heart disease.

Americans currently consume more than 3,400 milligrams of sodium daily, more than double the amount recommended by the AHA for ideal cardiovascular health.

“When you see this warning label, you know that that item has more than the total amount of sodium that you should consume in a single day,” city Health Commissioner Dr. Mary Bassett said Monday at an Applebee’s in Times Square as 40 of the chain’s New York City-area locations announced they had added the labels ahead of the deadline.

Chain restaurants constitute one-third of all restaurant traffic in New York City. Evidence suggests that health warnings increase knowledge and can lead to decreased purchase and consumption of certain products, according to the New York health department.

The menu labels are the latest health initiative pioneered by New York City, which also was one of the first to ban smoking, ban trans fats from restaurant meals and require chain eateries to post calorie counts on menus.

“New York City’s common-sense approach and gumption in its efforts to reduce sodium consumption should lead the way for public health officials across the country and in the Obama Administration,” Michael F. Jacobson, Ph.D., president of the Center Science in the Public Interest, said in a news release.

Even as health experts rejoiced, a legal battle loomed.

The National Restaurant Association said in a statement that it planned to file a lawsuit.

“While the Board of Health thinks they are targeting corporate chains, in reality they are dealing yet another blow to many of New York’s small businesses that have been working and continue to work hard to provide nutritional access to their customers,” Christin Fernandez, spokeswoman for the restaurant association, told PoliticoNew York. “That is why we are taking legal action against this latest assault which goes too far, too fast for New York’s restaurant community.”

Telephone and emailed requests for comment were not returned.

The National Restaurant Association has sued New York’s health department before. In 2012, when the city tried to limit the size of sugary drinks, the organization’s lawsuit blocked the regulation. The ruling never was implemented because the New York State Court of Appeals ruled the board “exceeded the scope of its regulatory authority.”