The West Papuan group applying to join the regional agency, the Melanesian Spearhead Group, says it would accept observer status but wants full membership.
The secretary general of the United Liberation Movement for West Papua, Octo Mote, says membership is needed to highlight the human rights abuses in the Indonesian region.
The leaders of the MSG, representing Papua New Guinea, Solomon Islands, Vanuatu, Fiji and the Kanaks of New Caledonia, meet this week in Honiara.
At least two of the countries are pushing for the ULMWP to get observer status.
Mr Mote says the decision is for the leaders to make.
"We will take any position the leaders think that that's the best, but of course, as a political leader myself I would fight for full membership, because we know that's the only way to stop this crime against humanity."