The standing committee of the UN's Convention on Endangered Species (Cites) is meeting in Geneva.
Key measures for the protection of endangered plants and animals will be decided at the five-day meeting.
Items on the agenda include Asian tiger farming, the export of mahogany from the Amazon basin and a proposal to allow China to import elephant ivory.
Environmental groups oppose the proposal, claiming China does not have adequate control of its ivory trade.
They say that allowing it to import ivory legally will simply fuel the illegal market.
The United Nations banned the trade in elephant ivory in 1989, and since then Cites has overseen the ban, allowing only one-off sales from four African nations - Botswana, Namibia, South Africa and Zimbabwe - whose elephant populations were judged to have stabilised.
Now China wants to import and trade that ivory.
Cites officials say China's enforcement of the laws on illegal trade in ivory are satisfactory.
But environmental groups disagree. They claim that elephant ivory is a booming black-market commodity worth hundreds of millions of dollars, and that China is the biggest customer.
Giving China the right to import more ivory legally will simply fuel the black market, critics say. They add that China's verification of where its imported ivory really comes from remains weak.
The discussions in Geneva are likely to be heated. Some environmental groups accuse Cites officials of ignoring the advice of their own wildlife experts, and bowing instead to pressure from China.