PHILADELPHIA — The city that invented that monument to gluttony, the cheesesteak, is ordering something new for the menu: one of the strongest restaurant labeling laws in the nation.

Philadelphia Mayor Michael Nutter on Thursday signed a bill that orders most chain restaurants to display calorie, fat and other information.

The law takes effect on Jan. 1, 2010.

The Philadelphia ordinance applies to restaurant chains with a total of 15 or more stores.

It will require their outlets in the city to tell customers about calories, saturated fat, trans fat, carbohydrates and sodium.

Because it covers more items and has fewer exemptions, it is stronger than laws passed in other places so far, according to Margo Wootan, director of nutrition policy at the Center for Science in the Public Interest.