WASHINGTON (AP) -- Diners will have to wait a little longer to find calorie counts on most restaurant chain menus, in supermarkets and on vending machines.

The head of the Food and Drug Administration says writing a new menu labeling law "has gotten extremely thorny" as the agency tries to figure out who should be covered by it.

The 2010 health care law charged the FDA with requiring restaurants and other establishments that serve food to put calorie counts on menus and in vending machines. The agency issued a proposed rule in 2011, but the final rules have since been delayed as some non-restaurant establishments have lobbied hard to be exempt.

The FDA has said the rules may come out this spring, but the agency may not meet that deadline.