BANGKOK - A plastic bag ban that came into effect last week to force shoppers to go green is threatening to sink makers of the environmentally unfriendly disposable in the red, even as plastic bag factories slash prices to woo retailers.

An agreement between the Thai government and major retailers across Thailand to stop providing free single-use shopping plastic bags came into effect on Jan 1 following publicity surrounding the deaths of marine life that had consumed plastic bags and a subsequent intense campaign against the products.

In August last year, an orphaned baby dugong "Mariam", which won hearts in Thailand, died from an infection. Bits of plastic were found in its stomach.

According to Greenpeace, Thailand is the world's sixth biggest contributor of ocean waste and produces more than 2.2 million tonnes of plastic waste a year.

"The ban is the only way we can tackle the issue," said Dr Thon Thamrongnawasawat, a marine biology professor at Kasetsart University.

Dr Thon, who helped the government draft the roadmap to ban and limit plastic products in Thailand, added: "Next to go are plastic straws and single-use plastic cups."

But even as environmentalists are hailing the initiative, Thailand's 1,000 plastic bag factories are suffering from the ban with some expecting to close down in months if the government does not provide some form of assistance.

"The effects are really severe," said Mr Naphat Thipthanakit, vice-president of the Thai Plastic Industries Association and the owner of a plastic bag factory near Bangkok which employs 160 workers.

Three in four of Mr Naphat's customers are retail chains and include malls, coffee shops and restaurants that joined the "Everyday Say No to Plastic Bags" alliance.

They have stopped ordering plastic bags from his factory since October last year, resulting in the loss of most of his 14 million baht (S$624,000) monthly revenue.

"The problem lies with the government's unclear messages and plans," he said, pointing out that the bags his factory makes can be reused many times, as they are up to 50 microns thick.

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But retailers just stopped ordering the bags.

"It's the thin single-use plastic bags of 12 microns that create problems for the environment, not the thicker bags like ours," he added.

According to Mr Naphat, to revamp the machinery so the factory can manufacture other plastic products would cost too much.

"I'd better give up on business and just retire. To reap the benefits of new investments will take too long for me," the 60-year-old, who has been in the trade for over 40 years, said.

To make matters worse for the manufacturers, eight TV channels signed an agreement with the Ministry of Natural Resources and Environment on Jan 2 to blur images and footage of single-use plastic bags.

Calling the censorship "very unfair", Mr Apiphop Phungchaikul, deputy secretary-general of the Federation of Thai Industries, said the current initiative is not the right answer, and that the key is to properly manage plastic waste.

The ban has sparked a chain reaction that has resulted in about a 30 per cent drop in customers, according to Mr Apiphop. It has forced manufacturers to slash their prices to woo shops that have yet to impose the ban.

The wholesale price is now 48 baht per kilogram compared to about 53-54 baht early last year, said Mr Tanatchai Lertboonyaphan, manager of Thai Hong Plastic.

His company supplies bags to mainly small groceries that have yet to participate in the programme.

"I predict that half of all the plastic bag factories will shut down in a few years," he said.