Two years after Thailand decriminalised cannabis in a giddy plume of publicity, businesses and free weed advocates say their dreams are about to go up in smoke, with the government poised to reclassify the plant as a narcotic by year-end.

Worse still, Thailand’s cannabis community fears the motivation is less based on legitimate concerns for public health, than appeasing big players eyeing domination of a sector potentially worth hundreds of millions a year once the law is changed.

On June 9 – the anniversary of decriminalisation – cannabis activists will rally near Government House in a “Return Cannabis Rights to the People” demonstration against what they say is a law reversal which will kick smaller businesses out of the industry.

“This move is driven by the ability to create exclusive regulations allowing only certain groups to cultivate cannabis, leading to a market value of tens of billions of baht,” said Kitty Chopaka, a leading Thai leading cannabis advocate, in an Instagram post on Friday.

There is a fear that “big cannabis monopolisation” will emerge, the post added.

Instead, activists want of a carefully constructed Cannabis Act to regulate use, protect young people and other groups from accessing weed and allow domestic businesses to grow.

Thailand peeled back years of stringent drug laws two years ago, ostensibly to allow for medicinal cultivation and use of the non-high parts of cannabis plant.

It was the banner political promise of the Bhumjaithai Party – Thailand’s third largest – and gave it a national profile. The party is in the governing coalition headed by Pheu Thai and does not agree with reversing the law.

But in the absence of a Cannabis Act defining who can grow and use cannabis and where, a vast market in recreational smoking has followed, including dispensaries or weed bars across virtually every city in the country.

While Thailand has become a beacon to weed smokers from across the world – and the first nation in Asia to roll back the law – the health ministry says the country is footing an ever-increasing bill for the impact of cannabis consumption on young and vulnerable people.

Prime Minister Srettha Thavisin, of the Pheu Thai party, appears set on relisting the plant as a category 5 narcotic by the end of the year, declaring in May the move would make it a crime to possess and consume cannabis.

The move has dismayed cannabis entrepreneurs who have ploughed money into businesses and followed the onerous licensing regulations to operate, which have flip-flopped over the last two years.

“Going from being a plant with medicinal benefit to be listed as narcotics, what’s the logic here?” said Apichai Techanitisawad, CEO of 66 Pattana Hemp Co.

Apichai said a Cannabis Act was needed to protect public health, but not recriminalise a plant – more so as countries across Europe moved into the same space.

“Why do they want Thailand to go backwards? Cannabis is a cash crop and my business is living proof. If you’re relisting as narcotics again, please make sure you have enough space in prison for 20,000 to 30,000 people – and enough money for reparations,” he added, saying the government must shoulder the responsibility to businesses and investors.

Srettha’s stated aim is to shut down – or at the very least carefully control – recreational use, but allow the medicinal and wellness market, mostly of low THC content, to continue to flower.

But punchy language on a new “war on drugs” and big claims on the health costs have alarmed Thailand’s blooming cannabis community, which lived underground for decades before the law was changed.

Since decriminalisation, weed advocates say the dividends promised to small farmers and businesses have failed to materialise. Farm gate prices have now collapsed as supply outstrips demand, something local cannabis entrepreneurs attributed to the excess buds from giant US grow rooms illegally entering the Thai supply chain.

In the absence of law, politicians have issued competing statements and threats, leaving investors in a spin.

The year-end deadline put on recriminalisation has added a new layer of insecurity to a business billed as being worth US$1.2 billion a year.

“I should imagine it would make stakeholders very nervous and investors reluctant until there is a solid footing to work on,” said Tian Scherer, founder of Thai Budtender Academy, which trains shops in the cannabis business and staff in selling the product.