Pheu Thai Party member Watana Muangsook and political activist Nuttaa Mahattana said on Monday that they would file lawsuits against those who posted online photos of them having sex.
Mr Watana, 61, wrote on his Facebook page that he would have his lawyer file suit against the owner of the hotel and other people involved in the incident.
He said the release of the photos on Friday was purely political.
The Pheu Thai logo was attached to all pictures in order to damage himself and the party, people who oppose dictatorship, he wrote.
It was the dirtiest of tactics to make such private pictures public, Mr Watana said.
Ms Nuttaa, 39, said that initially she had not intended to file a lawsuit, but an international human rights organisation advised her to do so, saying it could then use the case to support its campaign.
She would discuss the issue with her lawyer and file a complaint with police.
She said the photographed incident occurred about five months ago. She could tell because she was wearing a shirt that she rarely wears.
Ms Nuttaa said she had not tried to hide her relationship with Mr Watana. They went out and dined together in public.
She did not announce it because she did not want other parties to assume her political movement received support from a political party.
