Uproar peaked last week when South African President Cyril Ramaphosa had to delay his annual State of the Union address after lawmakers from the Economic Freedom Fighters (EFF) staged a protest in parliament, demanding de Klerk be removed from the legislature.
In a statement, ATM said De Klerk should be investigated for hate speech "and apply the appropriate sanction".
Former South African president FW de Klerk on Monday apologized and withdrew his statement that the country's former harsh system of racial separation known as apartheid was not a crime against humanity. But there's a difference between calling something a crime, like genocide is a crime.
In a letter addressed to SAHRC chief executive officer Adv Tseliso Thipanyane, ATM president Vuyo Zungula said de Klerk and his foundation had embarrassed the country's constitution.
On 14 February, the FW de Klerk Foundation issued a statement saying the idea that apartheid was a crime against humanity was "soviet agitprop". "He is an unrepentant apologist of apartheid; he is not willing to accept that apartheid was a crime against humanity", said EFF leader Julius Malema. While his comments - made earlier this month - have provoked outrage, African scholars have noted a sense of continental amnesia about the past, and say this misplaced nostalgia is not an exclusively South African phenomenon.
"I don't fully agree with that", de Klerk responded, adding, "I profusely apologize for [apartheid]".
"The ANC has consistently maintained, in line with the International Convention on the Suppression and Punishment of the Crime of Apartheid, that apartheid was and remains a crime against humanity", said Mabe.
"In terms of engaging with the FW de Klerk Foundation, we believe that that is the only way forward".
"I agree with the Desmond and Leah Tutu Foundation that this is not the time to quibble about the degrees of unacceptability of apartheid", the statement reads.
"In 1998 it was included in the Statute of Rome, which established the worldwide criminal court".
Following massive backlash, the foundation released another statement on Monday. "The nation is therefore indeed shocked, and we are all asking: Mr.de Klerk, was apartheid anything else than this definition by the entire world?" It can also be seen as the legislative expression of Nelson Mandela's statement during his inaugural address that "never, never and never again shall it be that this attractive land will again experience the oppression of one by another".