"Basil Rajapaksa with the blessings of Mahinda Rajapaksa is trying to cause a split in the SLFP," S B Dissanayake, Minister of Social Welfare said referring to the former president's brother.
Basil had organised a new movement of opposition groups from the central Badulla district during the weekend.
"This is action to cause a division than one to unify the party," Dissanayake, a Sirisena loyalist said.
Sirisena was handed the party leadership by Rajapaksa when the former defeated the latter in the January, 2015 presidential election.
Sirisena loyalists are branded traitors to the SLFP cause by Rajapaksa's supporters due to his alliance with the UNP.