NEW YORK — Customers at big fast-food chains in New York City are finally facing the facts about their meal choices. And for some, the truth may be hard to swallow — like 1,130 calories for a Big Mac, medium fries and a medium soda.

After months of resistance, the city's chain restaurants have begun obeying a first-of-its-kind rule requiring them to post calorie counts right on the menu.

McDonald's and Burger King were among the chains that unveiled new menu boards yesterday at scores of locations throughout the city, taking calorie information that had long been available on Web sites and tray liners and putting it front-and-center above the cash register.

The new rules are part of an anti-obesity campaign that has also included a recent citywide ban on artificial transfats in restaurant food. The regulation was first passed in 2006 but was redrafted after a court battle struck down the original version.

The calorie posting rule took effect in May, but legal action delayed enforcement until now. Starting today, chains big enough to fall under the rule will face penalties of up to $2,000 per store for not disclosing calorie information in a prominent spot on their menus, preferably next to the price.

Yesterday, the numbers at some restaurants could be hard to read, and many places only offered calorie counts for a few top-selling items. A few chains still appeared to be ignoring the rule, perhaps holding out hope that a court will block the plan, the first of its kind in any U.S. city. An industry lawsuit is pending.

Cathy Nonas, director of the city health department's physical activity and nutrition program, said some delayed posting the data because they were afraid customers might change their eating habits.

"We want to help people make an informed decision at the time of purchasing," she said. "Obviously, we have an epidemic of obesity across the nation, and New York City is no different."

Other chains, including Starbucks, Dunkin' Donuts and Wendy's, have been phasing in calorie information, store by store, for several months — surprising some patrons who had never realized that a single jelly doughnut has 270 calories, or that a grande mint mocha chip frappuccino with whipped cream packs a bigger caloric punch than a double cheeseburger.

Dietary guidelines for adults recommend about 2,000 calories a day, depending on age, gender and activity.

Still, some customers grabbing burgers, fries and shakes this week seemed not to notice the new columns of calorie data.

Audrey and Kevin Carroll, visiting from Toronto, didn't see that the box of treats they grabbed for the kids at Cinnabon on their way out of town contained a whopping 850 calories per bun.

"That's why they call it fast food," said their traveling companion, Cynthia Kaufman, of Long Island. "It's New York. If it's loud, and noisy, and you're in a hurry, and the kids are crying, who is going to stop and read the calories?"

To date, the lack of enforcement of the calorie-posting rules had meant haphazard compliance, and it remained unclear yesterday how many of the estimated 2,500 covered restaurants would meet the deadline.

A few restaurants appeared to be caught completely off guard by the calorie rules, especially the homegrown fast-food chains that pepper New York City's outer boroughs.

"This has been an absolute nightmare," said Enrique Almela, director of operations at Singas Famous Pizza, which has 17 restaurants, most in the borough of Queens.

The menu rule only applies to restaurants that serve standardized portion sizes and have 15 or more locations nationwide, a distinction intended to target fast-food giants. But in practice, the low threshold has swept up little-known outfits like Singas Famous Pizza and other local franchises that have never done nutritional testing before.

Almela spoke with The Associated Press from his car Wednesday as he rushed sample pizzas to a food laboratory. He said the calorie tests for his 35 different pizza combinations will cost $10,000, and he doubts they will produce accurate data.

"I may put 15 pepperoni on a pie. Someone else may put 12. We don't measure the amount of cheese we put on," he said. "If you put up roundabout numbers, how does that help anyone?"

The deadline also looked problematic for an unusual class of New York City eateries: loosely affiliated, largely immigrant-owned restaurants that share the same name and sometimes the same suppliers, but operate independently.

Afgan Paper & Food Products, which distributes food and packaging materials to many of the eateries, said it was scrambling to get them calorie info.

"The stores are all calling and asking for information. We don't have it," said Mariam Mashriqi, a company receptionist.

In the meantime, Mashriqi said, some owners were paying for the laboratory tests themselves.

"These are small stores. They are barely making a profit," she said.

City health officials said restaurants have had ample time to prepare. Every restaurant licensed by the city got a letter during the spring. Another 250 were issued formal warnings when health inspectors noticed that they hadn't yet complied.