Future Forward leader Thanathorn Juangruangruangkit has "invited" the party's supporters to rally in Pathumwan district of Bangkok on Saturday evening and demand "justice".
He made his call in a live one-minute video clip posted on his Facebook page on Friday afternoon, saying they should gather on the skywalk in front of the Bangkok Art and Culture Centre at 5pm.
"If you have had enough, do not want to tolerate these social conditions any longer and want to jointly push for a change, I invite everyone to attend," Mr Thanathorn said.
He wore a white shirt and a grey jacket showing the logo of his party and spoke in a gentle manner. The broadcast was made from an undisclosed, white indoors location. The camera shook a little bit, as if handheld by another person.
"It is time for us to sound the people's voice loudly, so that those in power can hear. If you agree with me that we, the people, must stand up and call for legitimacy, justice and equality in society, meet me on Dec 14," Mr Thanathorn said.
His call follows the Election Commission's decision on Wednesday to ask the Constitutional Court to disband the Future Forward Party on the grounds that its executive board accepted a 191-million-baht loan from Mr Thanathorn to fund its election campaign.
The Constitutional Court disqualified Mr Thanathorn as an MP last month for having shares in a media company when he registered his candidacy for the March general election.
In response, Prime Minister Prayut Chan-o-cha said security authorities would handle the situation. He asked if the rally was appropriate at a time of public happiness in the lead-up to New Year
“Is it someone’s personal issue? Is it also the issue of other people?” Gen Prayut said.
He said anyone with a knowledge of the law knew they would have to seek prior permission for a rally.
Manoon Wichiannit, the EC's director for investigation, and Sompol Pornpol, the commission's director for political party affairs, sent the request for the FFP's dissolution to the Constitutional Court on Friday.
They declined to answer reporters' questions.