New York diners curious to know how many calories are packed into the hamburger they just bought from White Castle or Wendy’s are out of luck.

The two popular fast food restaurant chains pulled posters listing calorie counts for menu items from the walls of their New York City restaurants and thus will avoid having to comply with a new mandate approved by the Board of Health that will affect thousands of New York restaurants.

The rule, which goes into effect July 1, will require about 10% of city restaurants to post calorie counts beside food items listed on their menus. The measure affects mostly chain and fast food restaurants, but only those providing calorie information to customers on or after March 1. By removing any calorie information from their New York City restaurants before the legislative deadline, Wendy’s and White Castle won’t be held to the same standard as other fast food restaurants in the city.

A spokesman for Wendy’s, Denny Lynch, said the company replaced its nutrition posters in New York earlier this week with new ones that include a wide range of nutrition information, including fat, carbohydrates, sodium, and protein, but not calories.

“We were forced to do it,” he said. “Complying with the regulation is way too difficult for us to do.”

Mr. Lynch said that because Wendy’s food is made to order and customers pick and choose side dishes and toppings for their meals, it would be challenging for the company to provide diners with every possible calorie combination. He said Wendy’s had been told it could post a range of calories on its menu, but Mr. Lynch said he thought that would likely confuse people and prompt numerous questions at the register.

The director of marketing for White Castle, Jamie Richardson, said the chain had been planning to take a close look at the nutritional information it displayed nationwide, and decided to remove its posters and brochures from New York restaurants before March 1.

“We wanted to allow ourselves as much flexibility as possible and ultimately work through a solution that is as customer-friendly as possible,” Mr. Richardson said.

The chairman of the City Council’s Health Committee, Joel Rivera, introduced a bill on Wednesday to ease the calorie posting rules. Speaker Christine Quinn has said she supports the new rule requiring restaurants to post the calorie content of menu items.

The director of nutrition policy at the Center for Science in the Public Interest, Margo Wootan, said the board of health’s new rule is “one of the strongest obesity prevention policies passed in any city or state.”

“I think it’s shameful that a restaurant would be decreasing the amount of information that they are providing when other restaurants across the country are working to increase it,” Ms. Wootan said.

A diner at a White Castle on Eighth Avenue in Manhattan, Ray Caceres, said he hadn’t noticed that the restaurant was no longer giving out nutritional information. He ordered two cheeseburgers and onion rings for lunch yesterday.

“It feels good on the way down, but not always afterwards,” he said. “That’s when I’d like to know how many calories I’ve eaten.”