The PPLF, which is headed by President Salva Kiir, was formed in 2010 after a national dialogue to unite leaders of all the political parties.
The PPLF says Ethiopia and Sudan should be removed from the mediation process.
It says the Compromise Agreement proposed by IGAD Plus is subjected to personal and national commercial interests from these two countries.
In statement, the group says it doubts that mediators from these countries can contribute to a genuine peace in South Sudan because their own countries are in conflicts.
The Minister of Cabinet Affairs, Dr Martin Elia Lomoro, spoke on behalf of the PPLF chairman.
“It is now our conclusion therefore that for peace to return to South Sudan, the entire IGAD Mediation team must be reconstituted,” Dr Lomoro said.
“While General Lazarus Sumbweyio may be acceptable, definitely Seyoum Mesfin and Mohammed Ahmed Mustaffa El-Daby must be replaced.”
The statement comes days after negotiators returned to Addis Ababa for the fourth round of peace talks.
Dr Martin Elia said the venue of the talks should also be relocated to Tanzania, Rwanda or South Africa.
“Not only that, but the venue of the peace talks be equally relocated to a country that has a rudimentary democracy and no rebellion,” he added.
He argued that these countries have a history of successful emersion from conflicts and would be good examples for South Sudan.
Other parties that are also members of the PPLF include the SPLM-DC, headed by Dr Lam Akol, the United Democratic Front, among others.
This group, now under the umbrella group known as the National Alliance, has disagreed with the government on key issues in the peace process, including the proposed Compromise Agreement.
Members of the national alliance were not at the press conference where the PPLF called for change of the IGAD mediators.