When the agency finally announced the rule last year, it was stronger and more sweeping than consumer advocates were expecting, covering food in vending machines and amusement parks, as well as certain prepared foods in supermarkets. The rule applied to food establishments with 20 or more outlets, from fast-food chains like KFC and Subway to sit-down restaurants like Applebee’s and The Cheesecake Factory.

Lynn Liddle, an executive vice president at Domino’s and chairwoman of the American Pizza Community, an industry group, said in a statement that the final rule had “serious deficiencies,” and that the trade group, which has lobbied vigorously against the rule, was putting its hopes in a House bill, the Common Sense Nutrition Disclosure Act, which it says would allow restaurants that take most of their orders online or by phone to label menus online rather than in stores. Another provision of the bill would limit coverage of the rule to establishments with more than half their revenue coming from prepared foods.

Margo Wootan, the director of nutrition policy at the Center for Science in the Public Interest, said that provision amounted to a loophole that would exempt supermarkets, convenience stores and movie theaters from having to provide calorie information to their customers for their prepared foods. She said a sponsor of the bill had promised to remove it.

The requirement applies to prepared foods — for example in salad bars or hot food bars in grocery and convenience stores — that are intended to feed one person. A sandwich or a salad would fall into this category, but not bulk items like loaves of bread or a rotisserie chicken.

The rule also covers alcoholic beverages. Beverages served in food establishments that are on menus and menu boards would be included, but a mixed drink at a bar would not, F.D.A. officials said last year.

Dawn Sweeney, the chief executive of the National Restaurant Association, said in a statement, “This standard makes good sense for the industry and our customers,” adding that “some of our members are ready to implement menu labeling while others still need more time.”

Daren Bakst, a research fellow in agricultural policy at the conservative Heritage Foundation, said it was not surprising that the implementation date for the rule had been extended, as grocery stores and convenience stores — establishments that he argued were not intended by Congress to be included — were probably struggling to comply as their products were less standardized than those at chain restaurants.