Shoppers who use money-off vouchers for the wrong item are shoplifters, according to a trade body representing some manufacturers of supermarket and high street products.
The Institute of Sales Promotion (ISP), which issued the statement, is concerned because its members, many of which are struggling during the economic turmoil, often foot the bill for invalid vouchers.
It wants to prevent consumers haggling with stores by using vouchers intended for a particular item to get a discount on a different product, and to stop them using expired vouchers, which supermarkets sometimes accept.
The ISP is currently seeking legal advice to determine whether it can prevent retailers, such as supermarkets, accepting illegitimate vouchers.
It is not seeking legal opinion on whether it can pursue shoppers through the courts, similar to record companies suing consumers who illegally download music. However, when asked, it refused to confirm or deny whether that may happen in future.
ISP chief executive Annie Swift says: "For a consumer to knowingly use a money-off coupon for a product they have not bought is the equivalent to shoplifting."
An ISP spokesman adds: "We are trying to educate consumers so they understand the effect using illegitimate vouchers has on businesses. They should stick to the terms and conditions and only use a valid voucher."
The MSE view is that where a voucher is used, unless you know it's fake, you bear no liability as an honest attempt to pay has been made.
Martin Lewis, creator of MoneySavingExpert.com, says: "The ISP is rightly trying to protect its members. Thatís its job, in the same way MSE's purpose is to show consumers how to save money.
"Yet to equate asking a supermarket to accept a voucher, even if youíre not buying the product, with shoplifting, is like saying Lewis Hamiltonís F1 driving breaks speeding laws. Afterall, nothing is hidden, there's nothing deceitful. It's a type of haggling.
"As far as consumers are concerned, the transaction is with the retailer and if the retailer accepts their method of payment, that's the end of it.
"While itís understandable manufacturers are unhappy if supermarkets then ask them for cash, thatís an issue between the two of them, and nothing to do with the consumer.
"For years, supermarkets have offered to accept vouchers they havenít issued."
If you get a coupon for 50p-off a particular item, for example, the retailer usually sends an invoice to the manufacturer of that item, for instance to Flora or Sony, to recoup the discount you receive.
The problems for manufacturers, says the ISP, come when an expired voucher is used, when vouchers are faked or inappropriately duplicated, or when a retailer accepts a voucher for the wrong product.
In the all above cases, retailers often invoice the manufacturer even where it has accepted an expired voucher or one for the wrong product.
Martin adds: "We are always careful to ensure customers openly ask to use the voucher, and caution against trying to slip it in unnoticed or use self-service checkouts. Care should be taken.
"Sadly, there are fake vouchers around, which is why any vouchers included in the daily updated supermarket coupons list are always checked for legitimacy."