Supporters of Thai Prime Minister Yingluck Shinawatra say they will take to the streets as moves to impeach her gather pace.
The Constitutional Court annulled the last election on Friday and the chairman of the Election Commission said it would be months before a new vote could be held.
This leaves the president at the head of an enfeebled caretaker government with limited powers.
There has been an eight-year battle between Bangkok's middle class and royalist establishment against supporters of Yingluck and Thaksin Shinawatra, her brother, who was ousted as premier by the army in 2006.
He lives in Dubai to avoid a jail term for abuse of power.
In the latest political crisis, 23 people have died and more than 700 have been wounded since November.
Speaking to an estimated 10,000 people in Pattaya southeast of Bangkok, another leader, Nisit Sintuprai, sent a warning to Suthep Thaugsuban, the former opposition politician who has led the protests against Yingluck since November.
"One big reason why we are on the move again is to tell Suthep that the majority in this country want democracy, want government through elections. We cannot accept a prime minister nominated by your people," he said.
Parties led by or allied to Thaksin Shinawatra have won every election since 2001 and Yingluck Shinawatra's Puea Thai Party is widely expected to win any election held under current arrangements.