Among the issues being thrashed out by trade ministers in Geneva are "special safeguard mechanisms" (SSM) that increase tariffs on agricultural products to protect domestic markets if imports surge above a certain level.
Latin American exporters such as Paraguay and Uruguay are at odds with fellow developing nation India which wants the measures to kick in at a lower level to protect its millions of subsistence farmers.
"There are still many problems to resolve, but the SSM is one of the main ones," World Trade Organization spokesman Keith Rockwell told AFP.
The issue is one of many sticking points in tortuous negotiations among ministers who are seeking to map out a new deal under the so-called Doha Round of talks by agreeing on cuts in subsidies and import tariffs.
The Doha Round was launched in the Qatari capital seven years ago but has been deadlocked because of disputes between the rich developed world and poorer developing nations, mostly over trade in industrial and farmed produ