Thailand permits the sale of ivory taken from captive elephants.
In a posting on his Facebook page, the star of Titanic and The Beach wrote that tens of thousands of elephants in Africa are killed by poachers each year to meet demand for their ivory tusks, which are often sold as carvings and bracelets in Asia.
"Much of the ivory trade goes through Thailand," the Tinseltown star wrote. "We can help save these beautiful animals. Join me and the World Wildlife Fund (WWF) and tell Thailand to ban all sales of ivory."
Bangkok will be hosting a conference by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (Cites), at the Queen Sirikit National Convention Centre from March 3-14.
Although Cites outlawed the international ivory trade in 1989, Thai law permits the sale of ivory from captive Thai elephants.
The ivory must be certified for sale by the Provincial Administration Department.
A WWF campaign, Hands off My Parts, has called on Thailand to end the sale of ivory from captive elephants.
Criminals can pass off illegally-obtained African ivory as domestic ivory and can sell it on the legal market, the WWF said.
The ivory trade here was the "largest unregulated ivory market in the world".
The National Parks, Wildlife, and Plant Conservation Department says ivory craftsmen and traders will face harsh legal action if they fail to meet new curbs set up to prevent the sale of illegal African ivory.
The new rules will require ivory shops to show their registration and certificates for raw ivory stocks, Theerapat Prayurasiddhi, the deputy chief of the department, said.
While Thailand permits the sale of ivory taken from domestic, captive elephants, officials say it is often hard to trace the origin of some ivory products sold here.
Sellers will also have to keep sales receipts and provide information about their buyers.
Mr Theerapat delivered the warning during a meeting with 200 ivory craftsmen and traders as part of the department's campaign to stop the country from acting as a hub for the illegal trade in wildlife. Sixteen more meetings will be held in the next two weeks.
"We want to show the international community that we are serious about the problem and we are taking action to solve it," said the deputy chief, who is well-known for his research on Thailand's rare wildlife.
The ivory trade in Thailand has been blamed for encouraging the killing of African elephants.
Ivory traders who fail to comply with the guidelines will be warned, he said. If the same offence is repeated, the Commerce Ministry would be asked to revoke their commercial registration, he said.
The violators could also face criminal charges and a fine of up to 40,000 baht and/or a jail term of up to four years if found guilty of involvement in the illegal ivory trade.
Ivory shops will also be asked not to sell ivory products to foreign buyers, as ivory products are banned from being exported, he said.
The products, however, are often smuggled out of the country, he added.
At least 270 pieces of ivory products were smuggled out of the country and have been seized overseas in the past few years.
The international community has criticised Thailand for failing to control the illegal business.
"Thailand never allows imports of African ivory and all ivory products produced and sold by craftsmen and traders must be from local, domesticated elephants only," Mr Theerapat said.
View the original story on the Bangkok Post here.