Some 3,000 of the National United Front of Democracy Against Dictatorship (UDD) members formed a 5km carvinal-like parade through the tourist town, inviting people to support democracy and holding placards denouncing independent organisations.
They were joined by tourists and students.
On stage later, 2,000 black balloons were released "in memory of" independent bodies, who they claimed had undemocratic attitude.
Jatuporn Prompan, the new UDD chairman, asked the red shirts all over the country to wear black for seven days starting Sunday as a symbolic move against all injustices.
A big rally is also planned on April 5, he said.
Thida Tavornset, Mr Jatuporn's predecessor, said the UDD disagreed with the Constitution Court's ruling on Friday to nullify the Feb 2 elections because the Constitution Court's acceptance of an ombudsman's petition was unconstitutional.
As well, she argued the election date was still one day — on Feb 2, 2014 — but voting dates could be several days such as for advance voting or when voting had to be re-run in constituencies affected by force majeure.
She added the ruling rewarded those who tore the charter while 20 million law-abiding citizens who cast the ballots were punished and saw their votes amount to nothing.