A few weeks ago we were waiting at a checkout counter in an Aeon supermarket and placed in the basket one of those laminated cards that say you don't need a shopping bag. When our turn came the cashier gave us a funny look and asked us if we really needed a bag for one item. We then read the card, which said that you should put it in your basket if you want a shopping bag.
We made a false assumption because we don't usually shop at Aeon. The supermarket we normally patronize asks you to indicate if you don't want a bag, and they'll knock ¥2 off the total if you do. Apparently, that practice is now giving way to the opposite tactic: You have to tell the cashier if you want a bag, in which case they will charge you for it.
Aeon, Japan's biggest supermarket chain, started this practice way back in 2007, and as of Nov. 1 every outlet follows the policy, which is ¥5 for an extra large bag and ¥3 for a large bag. Even Aeon's discount food chain, MaxValu, has adopted the charge-for-bags policy. For that matter, so has every other major supermarket chain. Ito Yokado charges ¥2 per bag, Uny ¥5, Seiyu ¥2 for a medium and ¥3 for a large, and Daiei ¥3 to ¥5, depending on the size.