Casac has filed an application to interdict NPA boss Shaun Abrahams from announcing whether former president Jacob Zuma will be prosecuted, pending a Constitutional Court ruling on an appeal in the case.
The possible charges against Zuma include fraud, corruption and racketeering.
In its papers filed with the ConCourt, the Council for the Advancement of the SA Constitution's executive secretary, Lawson Naidoo, argues that, if Abrahams takes a decision on the prosecution of Zuma, "there will be reasonable perception that his decision was biased".
He adds that Casac had repeatedly asked Abrahams to postpone the announcement, and he had refused.
"He has only given an undertaking that he will afford Casac two weeks notice before he announces a decision."
Abrahams gave Casac notice on February 26 - two days before the ConCourt heard the matter.
"Mr Abrahams has informed the applicants that his undertaking not to take a decision expires on 15 March 2018.
"Accordingly, this application is brought urgently and Casac asks that this court deals with it before 15 March 2018."
On December 15, North Gauteng Judge President Dunstan Mlambo ruled that Abrahams' appointment was questionable.
The court gave then-deputy president Cyril Ramaphosa two months to appoint a new head of the National Prosecuting Authority (NPA) after it declared the post vacant.
Zuma and the NPA appealed the ruling. However, following his election as president of the country, Ramaphosa withdrew the president's appeal.
The matter was heard in the Constitutional Court on February 28. Judgment was reserved.