Taiping MP Nga Kor Ming said he will rope in former prime minister Dr Mahathir Mohamad as a witness to testify for him against prime minister's wife Rosmah Mansor.

He said this is based on Mahathir who had made a similar statement via his blog of people complaining to him about Rosmah behaving like a prime minister.

“Why you do not sue Mahathir but only me? I will call Mahathir to the court as a witness,” Nga ( photo ) told Malaysiakini .

The Star Online today reported that Prime Minister Datuk Seri Najib Tun Razak and Rosmah has filed a suit against the Perak DAP chief for allegedly defaming them in a post on Facebook .

Their lawyer Mohd Hafarizam Harun said a copy of the claim which was filed last week will be served on Nga soon.

Asked about the case, Nga challenged both Najib and Rosmah not to run away from the court proceedings.

Najib and Rosmah must turn up in court

“I challenge Najib and Rosmah, come to the court, face-to-face to prove your case,” he said.

Nga also explained on why he refused to apologise to the duo as he was only making a fair comment as an MP.

He said the suit had shown that the freedom of expression in Malaysia has declined.

"As an MP, I do not even have a right to question," he added.

Nga is the third opposition MP to be sued by Najib after Petaling Jaya Utara MP Tony Pua and Pandan MP Rafizi Ramli.

Najib is the only serving prime minister to have sued opposition lawmakers.

The PM had also filed suits against PAS mouthpiece Harakah and this news portal.