South Africa's ruling African National Congress (ANC) has started its 3-day executive meeting as the Gupta business family is subject to more accusations of exerting undue influence. There are calls for Zuma to resign.
Zola Tsotsi, who resigned a year ago as chairman of state power firm Eskom, told the Mail & Guardian newspaper his exit had been orchestrated by the Guptas. The rich and influential family was accused this week of offering cabinet posts to two ANC politicians.
"Two months after the appointment, they called me and said they will have me fired because I am not playing the game. I was forced to resign shortly after that," Tsotsi told the newspaper.
The Indian-born Gupta family moved to South Africa at the end of apartheid in the early 1990s. Zuma has strong links to the family, but denies any of his decisions have been motivated by this.
A spokesman for the Guptas was not available for comment. The family earlier denied trying to influence political appointments and said they had been the victims of a politically motivated plot.
Matthews Phosa, a former ANC treasurer, claimed there was mounting evidence of an unhealthy relationship between the Guptas and Zuma. The president's son sits on the boards of at least six Gupta companies, Phosa said.
Zuma's opponents within the ANC
ANC Secretary-General Gwede Mantashe said on Thursday that the party had not discussed whether or not to remove Zuma.
"He's not untouchable; he's the president," Mantashe told Reuters. "Why should we see this as a crisis instead of a positive? It will embolden people to come to the fore ... so we can find the business people who are tampering within the ANC."
The financial newspaper Business Day said the ANC had to act to curb the Guptas' influence.
The Gupta family owns a business empire that includes computer equipment, media and mining interests. The family is alleged by the Rand Daily Mail to have worked closely with Zuma to secure interests in South Africa's nuclear energy sector.
The family supported Zuma during his struggle for the leadership of the ANC with then president Thabo Mbeki in 2005. The family's detractors often use the term "Zupta" to refer to their relationship with Zuma.
The current scandal, known as Guptagate, started in April 2013 when a planeload of 217 guests from India was cleared to land at a South African Air Force base for the marriage of Vega Gupta to Aakash Jahajgarhia.
It escalated again this week when Zuma denied suggestions that the Guptas might have been behind his sacking of the then finance minister, Nhlanhla Nene, in December.
Mmusi Maimane, the leader of the largest opposition party, the Democratic Alliance, has called on Zuma to resign after having failed to answer the question why Nene had been fired.
The ANC, which has been in government since 1994, faces a test of support at local elections in May.