The ANC said it was reconsidering its continued participation in the Western Cape legislature, The Times reported on Monday.
This was after one of its members was asked to leave the chamber because he refused to retract his statement that Helen Suzman aimed to "kill", according to the report.
Last month, during a debate on employment equity, African National Congress member Max Ozinsky said Suzman "wanted to kill us".
Western Cape Premier Helen Zille objected to Ozinsky's charge and asked deputy speaker Piet Pretorius to rule on whether it was parliamentary.
On Thursday, Pretorius ruled that Ozinsky's claim was unsubstantiated and could open the door to tit-for-tat accusations from across the aisle of the legislature.
"[The statement] goes beyond the scope of acceptable freedom of speech, is therefore not parliamentary, and needs to be withdrawn," he was quoted as saying.
Ozinsky refused to withdraw his statement.
The ANC on Thursday staged a walkout of the provincial legislature sitting. It claimed Pretorius's ruling was biased.
"We will call for a rules committee meeting where the speaker [Richard Majola] and his deputy are present early this week," ANC caucus leader Lynne Brown was quoted as saying.
The party also claimed that Pretorius's ruling was made under pressure from the Democratic Alliance.
ANC provincial secretary Songezo Mjongile said the party could not be part of an attempt by the DA to "sanitise" Suzman's role in apartheid.