NFU livestock board chairman Alistair Mackintosh said: "The UK unions and the IFA expressed total opposition to the recent decision by the EU Commission to re-open trade talks between the EU and the Mercosur countries of Brazil, Argentina, Uruguay and Paraguay.
"The European livestock sector needs the full support of the EU Commission to meet the challenges of climate change and food security across Europe.
"Re-engaging in these negotiations is contradictory to EU agricultural policy, which demands, among many things, that producers farm with increasing efficiency in order to reduce the effects of climate change while producing meat to the highest of animal health and welfare standards."
"In addition, South American production fails to meet EU standards across the important consumer issues of traceability, food safety, animal health and environmental controls."
The farmers also pledged to work together to ensure Single Farm Payments were fully protected in the planned changes to the Common Agricultural Policy post-2013.
Mackintosh said: "The farm organisations across the UK and Ireland were very clear that the SFP must be fully protected and paid to active livestock producers going forward."