The so-called Syrian National Council is against participating in the Jan. 22 talks because it says world powers have not done enough to topple President Bashar al-Assad.
The council is part of a broader opposition coalition which is due to make its final decision on whether to attend the Geneva on Monday.
A vote by the council to stay away would put further pressure on the fractious coalition, which has said it is ready to attend Geneva II peace talks in principle.
The talks are scheduled in less than three weeks in Switzerland, but details such as who will attend remain foggy.
Twenty-eight of 43 members of the council's decision-making body met on Friday and reaffirmed a decision against the talks that was made about a month ago. A formal vote was expected later on Saturday.
The council is seen as an influential voice in the coalition but Saturday's vote may turn out to have little effect on the coalition's final decision.
In November members of the coalition who were also members of the council voted in support of Geneva II, even though the council was against it.
The war in Syria started in March 2011, when pro-reform protests turned into a massive insurgency following intervention of western and regional states.
According to reports, the Western powers and their regional allies are supporting the militants operating inside Syria.
RA/SHI