The G77 meeting is to be held in the eastern city of Santa Cruz of Bolivia from June 14 to 15.
Nine parliamentarians from the Rajapaksa's ruling coalition have moved a condemnation motion in parliament against the UN Human Rights Council to appoint a panel to probe allegations of human rights violations during the final phase of the victorious military campaign against the LTTE.
Rajapaksa has said the parliament will decide whether to allow a UN panel in the country.
"The parliamentary party leaders would decide tomorrow the date on which this motion could be discussed in parliament", deputy speaker Chandima Weerakkody said.
The government has repeatedly said they would not cooperate with the investigation.
They accused the UN rights chief Navy Pillay of acting against her mandate.
The opposition has dubbed the motion a meaningless exercise.
"The government brought this situation upon themselves. Referring the issue to parliament would be useless," Vijitha Herath, a lawmaker said.
The international investigation came to be mandated at last March's UNHRC resolution which charged that Sri Lanka had done minimal to achieve national reconciliation with the Tamil minority.
