International conservation group World Wildlife Fund said in a statement Tuesday that DiCaprio sent a personal e-mail to his friends and supporters to encourage them to sign a petition addressing Prime Minister Yingluck Shinawatra over the wildlife trade.
In the e-mail, DiCaprio called on the Thai government to take the lead on elephant conservation by shutting down the ivory market.
Although Thai law prohibits sales of African tusks in the kingdom, ivory from domesticated elephants can be traded legally.
Activists say the loophole encourages massive quantities of African ivory to be illegally imported to Thailand each year.
