As customers increasingly bring their own bags to stores in response to the levy on plastic bags that began in July, guidelines for their use are being advocated to prevent shoplifting.

Earlier this month, a Tokyo-based antishoplifting organization made a poster urging customers to use baskets provided by stores when shopping and to keep their personal bags folded until check out. It also counseled keeping bags containing products from other stores sealed.

The move followed an alleged shoplifting case on Aug. 10 in which a man was arrested at a supermarket in Tanbasasayama, Hyogo Prefecture, on suspicion of stealing instant noodles after putting them into his personal bag.

According to a survey the nonprofit conducted in 2014, when incentives were already in place to encourage the use of personal shopping bags, 117 of the 511 retailers surveyed, or 22.9 percent, said they saw shoplifting rise as a result.

Retailers and security guards have expressed concern the problem could get worse as a result of the new levy on plastic bags. Japan's three largest convenience stores said three-quarters of their customers did not buy plastic bags in July.

Seven-Eleven Japan Co., Lawson Inc. and FamilyMart Co. sell their plastic bags for ¥3 or ¥5, depending on size.

"If everyone abides by the etiquette (in the poster), it will create an environment that makes it difficult for people" to use their bags for shoplifting, said Akira Mitsuzane, a senior official at the NPO. "We ask for shoppers' cooperation."

On July 1, Japan imposed mandatory charges for plastic shopping bags received at convenience stores, supermarkets, drugstores and other retailers as part of the global push to reduce marine pollution.

Japan generates the largest amount of plastic waste per capita after the United States, with plastic bags accounting for an estimated 2 percent of the annual 9 million tons of plastic waste it generates.