New York: A restaurant industry trade group is suing New York City’s Board of Health to stop it from enforcing a new rule requiring many chain restaurants to post warnings on menu items that are high in sodium.

The National Restaurant Association said on Thursday the Board of Health unfairly burdened restaurant owners and usurped the power of the popularly elected City Council by forcing restaurants with more than 15 locations nationwide to warn diners about salty foods.

Backed by Mayor Bill de Blasio, the rule, believed the first of its kind nationally, requires restaurants to post a salt shaker encased in a black triangle as a warning symbol next to any menu item with more than 2,300 milligrams (0.08 ounce) of sodium, the daily limit many nutritionists recommend.

New York City adopted the rule, which took effect on Tuesday, in an effort to help lower blood pressure and reduce the risk of heart attacks and strokes.

The rule also applies to concession stands at some movie theaters and sports stadiums. Violators would be punished by a $200 fine, starting on 1 March, 2016.

In papers being filed with the state Supreme Court in Manhattan, the restaurant group likened the rule to former Mayor Michael Bloomberg’s failed effort to curb sales of sugary drinks larger than 16 ounces (473 millilitres).

‘The regulation, like the Soda Ban before it, is completely arbitrary in its scope, reach, and application,’ the group said. ‘With the Sodium Mandate, the Board has required the disclosure of just enough inaccurate and controversial information about sodium in certain food items to cause far reaching negative consequences rather than help consumers and reduce public health risks.’

The papers could not be independently verified in court records.

Nick Paolucci, a spokesman for the city’s law department, said: ‘We are confident that the Board of Health has the authority to enact this rule. We will review the specific claims once we are served with the lawsuit.’

Bloomberg was known for pushing health initiatives in New York. Some, including requiring fast-food restaurants to post calorie counts and banning smoking in public places, have found growing acceptance elsewhere.

The National Restaurant Association calls itself the world’s largest food service trade association, supporting more than 500,000 restaurant businesses.

The case is National Restaurant Association v. New York City Department of Health & Mental Hygiene et al, New York State Supreme Court, New York County.