The anti-government Pitak Siam group will call off its rallies if its next demonstration attracts less than 1 million supporters.
Group leader Boonlert Kaewprasit said Sunday that the number of participants in the next rally will decide whether the movement continues to stage public demonstrations.
If it attracts less than 1 million people, the approach will be scrapped, he said, although the group will continue to attempt to overthrow the Yingluck Shinawatra administration through other means.
The next rally is scheduled for later this month. The date has yet to be confirmed.
Gen Boonlert shrugged off criticism that the anti-government demonstration will be unsuccessful, saying that its critics should wait and see.
There is no official attendance tally from the first demonstration, held on Oct 28 at the Royal Turf Club in Nang Loeng. Organisers claimed that roughly 20,000 people turned out, but police said the number was closer to 7,000.
Gen Boonlert said he welcomes members of the anti-Thaksin Shinawatra yellow-shirt group, although its core leader Sondhi Limthongkul has said he will not be joining the next rally.
A pro-government group led by a red-shirt outfit is planning a counter-rally in Samut Prakan on Nov 18 to express their support for the third reading of a constitution amendment bill.
The Pitak Siam leader brushed aside concerns that the two groups could confront each other.
Gen Boonlert said Pitak Siam's demonstration will be peaceful and lawful.
He also reiterated that privy councillor Surayud Chulanont was not involved in the Pitak Siam movement.
Some observers had linked Gen Surayud to the anti-government rally as Gen Boonlert and Gen Surayud were classmates in Class 1 of the Armed Forces Academies Preparatory School.
"I do not want Gen Surayud to be involved and he has no link to it," Gen Boonlert said.
Gen Surayud on Saturday assured he had no involvement with the group.
Meanwhile, Pheu Thai Party list-MP Chaovalit Vichayasuth, who is also a secretary of a parliamentary committee on reconciliation study, called on members of Pitak Siam to consider the possible consequences of their rally.
He said the group should follow democratic rules in seeking to topple the government.
A military coup, which the group was asking for, would cause a setback for the country, he said.
Mr Chaovalit also shrugged off the threat made by several kamnan and village headmen from 17 northern provinces to join Pitak Siam.
The local leaders have vowed to stage a protest in Bangkok on Wednesday to oppose the government's plan to issue a law requiring them to retire at 60 instead of being able to hold on to the position for life.
Mr Chaovalit said Yongyod Kaewkiew, chief of the kamnan and village headman association, had promised that his group would not participate in the Pitak Siam rally.
The group will only go to Siriraj Hospital to offer their best wishes to His Majesty the King, Mr Chaovalit said.