Both the party and Amunugama believe president Sirisena to be the only candidate who could gain most of the 27 per cent minority votes in the country, he told BBC Sandeshaya.
The president, who chaired the meeting, did not comment on the party decision.
The prevailing political situation is different to what had existed on 09 January 2015, when Mr. Sirisena took oaths in his office and declared that he would not seek a second term, said Amunugama.
The SLFP CC has also agreed for the full implementation of the 13th amendment to the constitution that gives land and police powers to provincial councils, he also said.
Instead of a new constitution, the existing one should be amended, the party has also decided.