The Syrian High Negotiations Committee (HNC) and Head of the dissidents' negotiating team Nasr al-Hariri protested at the Saturday meeting held in Saudi Arabia.
The opposition-affiliated media described the meeting as a coup against the negotiating team.
The Arabic-language al-Madan news website quoted al-Hariri as saying that he does not recognize the meeting, and the 'independent dissidents' does not have any meaning to him.
He questioned the legitimacy of the meeting which did not even invite him as the head of the negotiating team.
The HNC had also in a letter on Thursday called for cancelling such a meeting but Riyadh did not pay attention to the demand.
Meantime, the Arabic-language al-Arabi al-Jadid news website reported that the Riyadh meeting was aimed at isolation of Turkey-affiliated members of the HNC to decrease Ankara's influence.
It added that the Saudi government had also invited new figures of the Syrian Kurds to the independent dissidents' meeting.
The HNC was founded in December 2015 at a conference held in Riyadh, Saudi Arabia, which was attended by around 100 delegates. At the end of the conference, a joint statement was issued to confirm the formation of "a High Negotiations Committee for the Syrian Revolution and Opposition Forces (HNC), with its headquarters in Riyadh, to undertake the tasks of choosing a negotiating delegation and to act reference point for negotiators with the representatives of the Syrian regime on behalf of the participants".
The HNC, led by Nasr al-Hariri, participated in the Geneva peace talks on Syria.