PAS secretary-general Takiyuddin Hassan has instructed the party at all levels to ensure "maximum" turnout at the rally against the International Convention on the Elimination of All Forms of Racial Discrimination (Icerd).
In a letter to all PAS state chiefs, wings and divisions nationwide, Takiyuddin asked party members to be present at Dataran Merdeka from 1pm to 6pm on Dec 8.
"All PAS leaders and members at the state, division and branch levels as well as wings are instructed to mobilise en masse to attend the rally as well as to urge and invite the maximum number of PAS supporters to the programme to express solidarity on the issue," read the letter.
The letter also listed three gathering points before converging on Dataran Merdeka, namely Masjid Negara, Masjid Jamek and Sogo shopping centre in Kuala Lumpur.
It said PAS president Abdul Hadi Awang and Umno president Ahmad Zahid Hamidi would also be present.
The event is organised by Gerakan Pembela Ummah, a coalition of Islamic NGOs, but has received backing from Umno and PAS.
The letter stated that the objective of the rally would be to express thanks for the government's decision not to ratify Icerd and ensure that the attempt to ratify the United Nations convention is not revived.
It added that the rally is also to protest any threats to the Islamic, royal or Malay institutions.