A law body headed by former judge Johann Kriegler intends challenging the Judicial Service Commission's decision not to probe Cape Judge President John Hlophe.
The pending legal challenge by Freedom Under Law has the support of two of its panel members, Archbishop Desmond Tutu and Dr Mamphela Ramphele, Kriegler, a former Constitutional Court judge told a media briefing in Johannesburg on Thursday.
"The two did not only empower me, but asked me to express in public, the grave seriousness of . The rule of law will not survive if the legitimacy of the judiciary in not protected," he said.
The JSC's decision not to probe allegations that Hlophe tried to influence Constitutional Court judges in a ruling involving President Jacob Zuma's former corruption case was "gravely harmful to the rule of law".
"The decision by the JSC is the biggest threat to rule of law the country has experienced since is emerged from darkness," Kriegler said at the Women's Jail at Constitution Hill.
He said "unequivocally" that the purpose of the legal challenge was not to have Hlophe impeached, but to compel the JSC to do its duty.
"I owe nothing, I bare him no grudge, I owe a duty to the judiciary of this country which I have served for decades to the best of my ability."
The JSC's decision was "irrational and unreasonable" and it had already impaired the nomination process for new Constitutional Court judges.
One judge had already withdrawn his nomination as he was not prepared to submit his candidacy "to the deliberation of people he did not trust".
Launched in January the FUL, registered in South Africa and Switzerland, was aimed at promoting democracy under the law "and to advance the understanding and respect of the rule of law and the principle of legality".
The justice department on Wednesday said Hlophe would return to work on Monday after being placed on special leave in May 2008.
The JSC criticised Hlophe for raising pending judgements in President Jacob Zuma's former corruption case with Constitutional Court judges Bess Nkabinde and Chris Jafta, but said it did not find evidence that he tried to influence them.
Opposition political parties condemned the decision.
In a public lecture last month, Kriegler described Hlophe as a "manifestation of the problem" with the judiciary, warning that judicial independence should not be sacrificed on the "altar of transformation".
Hlophe was recently nominated for a post as Constitutional Court judge. His supporters hoped he would fill the shoes of Chief Justice Pius Langa when the latter retired later this year.
He was described by the Justice for Hlophe Alliance - a lobby group supporting him - as the best candidate to promote transformation of the judiciary in the country.
However, President Jacob Zuma last month nominated Judge Sandile Ngcobo for the post.
Other FUL directors include Elize Angula, a Director of Lorentz Angula Incorporated, practising in commercial litigation, human rights law and family law; former dean of law at the University of Cape Town Professor Hugh Corder; Ezra Davids, a partner in and head of Bowman Gilfillan's corporate department and Jeremy Gauntlett SC, co-chair of the IBA's Forum for Barristers and Advocates.
Its international advisory board included Sir Sydney Kentridge, a member of Nelson Mandela's defence team in 1961; businessman Cyril Ramaphosa, Dr Mamphela Ramphele, former attorney general to India Soli Sorabjee SC and Archbishop Desmond Tutu. - Sapa