The DA is considering laying criminal charges against ANC secretary general Gwede Mantashe, Eyewitness News (EWN) reported.
This follows remarks by Mantashe that party members were not "free agents" who could vote with their consciences, come the vote of no confidence in the president on August 8.
DA chief whip, John Steenhuisen reportedly said Mantashe could be in contravention of the Powers, Privileges and Immunities of Parliament Act, which makes it an offence to coerce, threaten or intimidate MPs.
"We will be exploring various options in terms of how we'll hold Mr Mantashe accountable for his violation of this Act," Steenhuisen was quoted as saying.
Meanwhile, ANC MP Mondli Gungubele was asked to stop making public statements about the motion of no confidence vote. In a statement on Tuesday, the ANC in Gauteng said:
"After affording comrade Gungubele an opportunity to explain himself, he was advised and requested to desist from making public pronouncements on the matter."
Gungubele had said he would support a motion of no confidence vote, adding that he had lost confidence in Zuma.
The ANC in KwaZulu-Natal is pursuing ill-discipline charges against MP Makhozi Khoza for her comments, calling on Zuma to resign.