ANC chairperson Gwede Mantashe's proposal to put a 12 000-hectare ceiling on land ownership has been slammed by the black farmers' union, the Freedom Front Plus and Agri SA.
The National African Farmers' Union (NAFU) said the proposal was neither practical nor economical.
"It is not going to work," NAFU president Motsepe Matlala said.
Mantashe proposed that the Constitution be amended to limit land ownership to 12 000 hectares per farm owner and that white farmers who own more than that hand over the rest to the state without receiving any compensation.
He spoke to News24 exclusively on Tuesday.
Matlala said a similar proposal was first made by former rural development and land reform minister Gugile Nkwinti about three years ago at a conference in Pretoria.
"I am not being silly here, but from a practical and economical point of view, it will not work. You have for example, commodities that require large amounts of land," he said.
Matlala added that a cap on land ownership would affect food production because only 10 percent of farmers were currently feeding the nation and exporting to international markets. He said it would also lead to job losses.
He cited as an example, a few farmers owning between 50 and 100 thousand hectares of land were producing 14 million tons of maize annually for local and export consumption. A ceiling on land ownership would also affect black farmers, he said.
"It is going to affect black and white farmers and it is also going to affect production because the argument is that there are only between nine and 12 percent that really feed SA and export agricultural produce. So clearly, if you are going to curtail them, it means that the production will be lowered and quality will also be poor," Matlala said.
The Freedom Front Plus said the ceiling suggestion showed how "dangerously ignorant" the ANC was about land.
"Mantashe's statement is thoughtless and only goes to show that the ANC itself does not even know how to implement expropriation without compensation. The ANC is grabbing at straws in an attempt to promote a populist ideology by creating unrealistic expectations with its supporters," FF Plus leader Dr Pieter Groenewald said in a statement.
Groenewald challenged the ANC to release its full plan to implement its December 2017 resolution to expropriate land without compensation.
"So that everyone can see for themselves that it is unrealistic, that it will only destroy the economy and that it will surely jeopardise food security," he said.
The ANC decided earlier this month to support the amendment of the Constitution to make it explicit to allow expropriation of land without compensation.
Meanwhile, Agri SA President Dan Kriek said Mantashe's suggestion was "irrational and not carefully considered.
"A one-size-fits-all approach goes against established agriculture principles as commodities and farming practices differ in land use. Different crops or animals require different sized farms to be financially feasible. A 12 000-hectare farm in the Karoo would barely be sustainable." Kriek said.