You may be referring to a federal law concerning the labeling of foods with a "characterizing" flavor. (Although, states often incorporate federal food labeling laws in their own food law statutes.) Title 21 of the Code of Federal Regulation (CFR), Section 101.22, provides that if the label, labeling, or advertising of a food makes any direct or indirect representations with respect to the primary recognizable flavor(s), by word, picture or other means (e.g., "vanilla" pudding), such flavor shall be considered the characterizing flavor. In addition, if the food contains any artificial flavor that simulates, resembles or reinforces the characterizing flavor, the name of the food on the principal display panel must be accompanied by the common or usual name(s) of the characterizing flavor, in letters not less than one-half the height of the letters used in the name of the food, and the name of the characterizing flavor must be accompanied by the word(s) "artificial" or "artificially flavored", in letters not less than one-half the height of the letters in the name of the characterizing flavor (e.g., "artificial vanilla", "artificially flavored vanilla", or "vanilla artificially flavored").