The Federation of National Organisations (FNO), has warned against the 'separatist' agenda being pushed through the calls for the 13th Amendment.
Gunadasa Amarasekera, whose Patriotic National Movement - an ally of the National Freedom Front - is a member of the FNO, said the 13th Amendment must be "pruned".
"The UNP and the SLFP are using the idea of a national government to push the country to ruin by making way for the Eelam to take over," he said.
"No one can protect the country because the opposition will also agree to whatever decision the UNP reaches."
The FNO is made up of political organisations, businesses and civil society groups based in the south.