Anti-coup campaigner Sombat Boonngamanong has vowed to fight the Election Commission's refusal to approve the registration of his Grin Party (or Krian Party in Thai) which translates as "The Firebrands' Party".
Sombat: We want a fight
Mr Sombat said he will take the case to the Administrative Court.
On Friday night he posted on Facebook a letter sent from the EC rejecting his request to register his party along with a message saying he would take this opportunity to set a new standard by bringing the matter to court.
"In the battle in the Administrative Court, I expect to see a debate that will be supported with reasons rather than this imagination. See you in court. Grin Party won't be focusing on wooing voters but picking a fight," he wrote on his Facebook page.
In the post, Mr Sombat also accused the EC of making a subjective judgement in deciding that the name of his party is against moral principles as it picked only one out of three meanings of the word krian in Thai.
The party had previously emphasised several times that the name krian in this case means short, tidy, fitted and clean, he said.
"This matter may not be a big deal to some, but we think it's totally a matter of rights and freedom in naming a political party," he said.
Meanwhile, Thanathorn Juangroongruangkit, founder of the Future Forward Party, announced in a Facebook live broadcast on Friday night that the party's first formal meeting is scheduled to be held in the afternoon of May 27 at Thammasat University.
The party plans to send 1,500 invitations.