The decision not to prosecute Deputy President Jacob Zuma reflected badly on the reputation of South Africa's legal system, said the Democratic Alliance's Sheila Camerer.
"Director of Public Prosecutions Bulelani Ngcuka has been subjected to unbearable political pressure over the past weeks.
"The DA's objections to placing ANC (African National Congress) politicians in positions like that of the director of the National Directorate of Public Prosecutions - positions that are required by the Constitution to be completely independent and impartial - seem fully justified," Camerer said in a statement on Saturday.
Her comments followed Ngcuka's announcement earlier in the day that Zuma would not be prosecuted for anything related to South Africa's multi-million rand arms deal.
This was despite a recommendation from the investigation team that criminal prosecution be instituted, Ngcuka said.
Camerer said: "The president became involved, the African National Congress was deeply involved and so was Mr (Cyril) Ramaphosa. The so called 'plea bargain' - mooted before Mr Ramaphosa's visit with Mr Ngcuka - has now come about, clearly pointing to Mr Ramaphosa's involvement despite his claims to the contrary.
"All of this constituted improper interference with the judicial process and now casts a blight over the decision not to prosecute the deputy president," said Camerer.
ANC member Cyril Ramaphosa had previously said he had been asked to mediate in the ongoing arms deal dispute. Last Sunday he announced he would not play any role in the saga.
"The investigation process should have been impeccable but it was not. The suspicion will linger that ANC big wigs are somehow above the law and that the minnows like Tony Yengeni and Schabir Shaik are 'fall guys'," she said.
Ngcuka also announced that Zuma's personal financial advisor, Schabir Shaik, would be charged with various counts of corruption, fraud, theft of company assets, tax evasion and reckless trading. The Nkobi group of companies, of which Shaik is a director, and French arms company Thomson CSF would be prosecuted for contraventions of the Companies Act.
Issues around the declaration of gifts and donations received by Zuma would be referred to Parliament for its consideration. - Sapa