When your distributor or store that will sell your product requires it. There is no law that says you must bar code a product. However, many national retail chains, like Walmart, Fry's, Bestbuy, and Sam's Club require all products they sell to have a bar code that is unique for the specific product. The stores require this "source marking" because it is easier for the company that makes the product to mark it rather than the store. If you don't have a bar code on the product, these stores will not sell the product.