
Somjate and deputy director Anthony Brooke said the impact of the US legislation, aimed at slapping economic sanctions against the Burmese junta, had already resulted in up to 100,000 job losses in Thailand.
The gem and jewellery sector is currently one of the country's top-three foreign-exchange earners, with overall 2008 shipments amounting to more than US$8.2 billion (Bt290 billion).
The industry employs more than 1.1 million workers in the upstream, midstream and downstream sectors. Of the total, 726,000 workers are employed in the upstream sector, which involves gem heating, cutting and polishing.
The midstream sector, which includes jewellery design, casting, setting, polishing, quality control and packing, employs about 400,000 workers.
The downstream sector - distribution and sales - has about 40,000 workers.
During the first quarter, shipments to the United States, the largest market for Thai gems and jewellery, accounting for 25-30 per cent of the sector's exports, fell 40.2 per cent to $155.3 million, from $259 million in the same period last year.
"The US recession has hit demand, but the impact was compounded by the Tom Lantos ruby ban," said Brooke.
Somjate said exports had started to fall sharply last October following the enforcement of the Tom Lantos law the previous month.
Most of the 1,700 TGJTA members have found it hard to get alternative sources of raw gemstones. Thailand imports about 20 per cent of its rough stones from Burma.
Somjate said the US had ignored World Trade Organisation rules on country of origin, under which products that have undergone a substantial transformation in Thailand should be classified as having Thai origin.
Instead, the US Congress passed the Tom Lantos law last year, focusing on economic sanctions against the Burmese junta. This resulted in Burmese raw materials, including rough stones, effectively being banned in the US market.
In a bid to redress the situation, the TGJTA has urged the government to negotiate with Washington to review the law.
In addition, it has backed its counterpart associations in the US, comprising importers and retailers of Thai jewellery, to help lobby for legislative changes.