Click here for more coverage of Syria's war from Al Jazeera
Its military arm, the Supreme Military Council (SMC), has been eclipsed by Islamist rebels and Al-Qaeda-linked fighters. It was not immediately clear whether the coalition's vote would be backed by a separate meeting, in Ankara, of Syrian rebel militias, who would be needed to implement any agreements made at peace talks.
Syrian officials have pledged to attend the Jan. 22 Geneva II talks, though they dispute the invitation letter's focus on setting up a transitional authority, saying the priority is "to continue to fight terrorism" — a phrase they use to describe Assad's battle with increasingly radical rebels.
One of the main demands of the opposition was that Assad agrees to step down before going to the conference. With his government troops keeping their momentum on the ground, Assad's government has said he will not surrender power and may run again in elections due in mid-2014.
The U.S. and Russia have been trying to hold the peace conference since last year, and it has been repeatedly delayed. Both sides finally agreed to sit together on the negotiations table after dropping some of their conditions.
Syria’s mainly Sunni Muslim rebels have been battling for nearly three years in an attempt to overthrow Assad, whose Alawite sect is an offshoot of Shia Islam and makes up about 12 percent of Syria’s 23 million people. The conflict erupted in 2011 with a violent crackdown on peaceful protests against four decades of Assad family rule.
Al Jazeera and wire services