NEW YORK (CNN) -- The New York City Board of Health voted unanimously Tuesday to require all city chain restaurants to post calorie data on their menus.
The order requiring New York chain restaurants to post calories on their menus comes after months of litigation.
Some restaurants already make the calorie counts of menu items available, but beginning March 31 they will have to put the numbers on menu boards and menus.
The change will affect restaurants with 15 or more outlets -- roughly 10 percent of all city restaurants, according to a news release from the city's health department.
The Department of Health argued in October that "calorie information provided at the time of food selection would enable New Yorkers to make more informed, healthier choices."
The expectation is that the information will help combat obesity in New York, a city in which 54 percent of adults are overweight or obese, according to a 2005 Community Health Survey. 
Watch Dr. Gupta explain the new calorie rule. »
"Today, the Board of Health passed a regulation that will help New Yorkers make healthier choices about what to eat; living longer, healthier lives as a result," Dr. Thomas R. Frieden, city health commissioner, said in the news release. Paging Dr. Gupta Blog: Will seeing numbers change your eating habits?
The mandate comes after months of litigation. The New York Restaurant Association sued the Board of Health in an attempt to block the measure, claiming it would violate its members' First Amendment rights.
Chuck Hunt, spokesman for the association, said the group is "considering options, one of which is the intent to pursue further litigation against the city." E-mail to a friend 
-- From CNN's Nkechi Nneji
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