In a leaked document, Mbeki criticised the ANC's approach to land reform, which he said was not in line with the governing party's non-racial character.
Mbeki was responding to the ANC's push for the expropriation of land without compensation, which the party adopted as a resolution at its 54th national conference last year.
Independent Media has reliably established the authenticity of the document.
The former president said the position the ANC had taken on the contentious land issue raised important questions about the strategic definition of the ANC as a representative of all the people of South Africa, as envisioned by the "people's document", the Freedom Charter.
He said the party had been asserting that it had historically acted as a representative of all South Africans, black and white, but that the current leadership was moving away from the claimed character of the party, moving closer to the PAC and EFF.
On Tuesday, EFF national spokesperson Mbuyiseni Ndlozi lashed out at Mbeki, accusing him of defending white domination.
He said Mbeki jumped into defending white land domination as “he realises that we (black people) are united on the question of land in this country for the first time".
“He has taken to paper, but when Marikana happened, resulting in the death of over 40 mineworkers, Mbeki never released an essay.
"Mbeki never wrote more than 3000 words to question the legitimacy of the ANC policies when Life Esidimeni happened, claiming the lives of many of our people,” he said.
Ndlozi said although the EFF would never change its stance on the expropriation of land without compensation, it would never call for white people to be chased out of the country.
ANC national spokesperson Pule Mabe did not respond to questions by the time of publication.
The Thabo Mbeki Foundation also did not respond to questions on the issue, as well as on the origins of the document.
Mbeki said that by making the land issue a race issue, the ANC had abandoned its role of being the representative of all South Africans.
“Certainly, the argument that has been advanced by the ANC leadership since the 54th national conference at Nasrec last December about the land question communicates the firm statement that the ANC has changed in terms of its character.
"It is no longer a representative of the people of South Africa,” Mbeki said.