A report from the department said it is revising the Customs Code to collect more tax on such products, many of which are hugely popular - especially with women - and sold without proper controls.  Many of the products hit the shelves before receiving approval from the Food and Drug Administration. Moreover, they are often sold with false claims that they can improve health and appearance.

The department will reclassify the products so that they can be taxed at the same rate as luxury products - up to 20 per cent. The government will decide the actual rate for the two categories.

The plan has provoked criticism from companies that sell such products. Panuwat Chonwittayasittikul, the sales manger of Scotch Industrial (Thailand) Co Ltd, which makes Scotch bird nest and chicken essence beverages, said a 20-per-cent tax rate would be too high.

Makers of food supplements already have high operating costs, he said, and the new regulation would add to the lengthening list of negative factors affecting manufacturers.

However, Nalinee Paiboon, president of Giffarine Skyline Unity Co Ltd, which sells food supplements directly to customers, said a 20-per-cent rate was not too high. The tax revision might affect her company slightly as it imports some semi-finished products from Germany.

The department is also revising the Customs Code to collect more tax on beverages, including extracts and concentrates.

"The plans to collect additional tax ...  are not set to achieve the government's tax collecting goal. We want to adjust tax for all necessary categories and limit consumption of unnecessary products", said an official who asked not to be named.