Otai Reformis has set four conditions for its support to Pakatan Harapan's stand to work with former prime minister Dr Mahathir Mohamad to oust Prime Minister Najib Abdul Razak.

Firstly, Mahathir must support the struggle in freeing jailed PKR de facto leader Anwar Ibrahim, Otai Reformis chairperson Saari Sungib said in a statement today.

"Mahathir should support all the measures taken to recover the judiciary system and he should reject the draconian laws.

"He should voice out for the reinstatement of human rights," the Hulu Kelang assemblyperson from Parti Amanah Negara said.

Otai Reformis is a group of activists from the Reformasi era which first emerged to opose the Red Shirt rally in September last year.

Harapan has agreed to work with Mahathir in its quest to topple Najib, but said it would not form a coalition for the action.

Mahathir, who resigned from the party he has led for two decades last week, will sign a declaration seeking the removal of Najib with several Harapan leaders today.

Anwar has also called on the people to support this effort and to set aside "personal vendettas".