The third was investment bank Sasfin, which said it had decided to cut links with Gupta mining firm Oakbay Resources and Energy (>> Oakbay Resources and Energy Ltd) in March, two days after a newspaper suggested they may have had a hand in Zuma's sacking of finance minister Nhlanhla Nene in December.

Sasfin's relationship with Oakbay will formally end on June 1, a Sasfin spokeswoman said. The decision had not previously been made public.

Zuma has denied numerous allegations of the Guptas wielding undue influence. The Guptas have also routinely dismissed reports of their influence, saying they are pawns in a political plot to get Zuma out of office.

After the newspaper report last month, Deputy Finance Minister Mcebisi Jonas said the Guptas had offered him the top job at the Treasury before Zuma fired Nene. The Guptas also denied that allegation.

In an email to KPMG staff seen by Reuters, local chief executive Trevor Hoole said he had decided to stop auditing Oakbay after consulting regulators, clients and KPMG's internal risk departments.

"I can assure you that this decision was not taken lightly but in our view the association risk is too great for us to continue," Hoole said in the email.

"There will clearly be financial and potentially other consequences to this, but we view them as justifiable."

Oakbay confirmed the end of the 15-year relationship and said it understood it had been a "very reluctant decision" for KPMG. A KPMG spokesman declined to comment.

Barclays Africa (>> Barclays Africa Group Ltd), which runs South Africa's biggest retail bank, Absa, also confirmed it no longer had a relationship with Oakbay, which is valued at 16 billion rand (763 million pounds) on the Johannesburg stock market.

In an annual report from last August Oakbay listed Absa as its bank. An Absa spokesman declined to comment any further.

The three Gupta brothers moved to South Africa from India at the end of apartheid in the early 1990s and went on to build a business empire that stretches from technology to the media to mining.

They have also forged a close personal relationship with Zuma, whose son, Duduzane, sits on the board of at least six Gupta-owned companies, according to company registration papers.

Parliament will on Tuesday debate a motion to impeach Zuma after a top court ruled the president had violated the constitution by ignoring orders from the public protector that he repay some of the $16 million in state funds spent to renovate his private residence at Nkandla.

Zuma says he never knowingly or deliberately set out to violate the constitution.

The Africa National Congress majority in parliament will almost certainly give Zuma political cover against the attempt to impeach him. But the judicial rebuke may embolden anti-Zuma factions within the ruling party to mount a challenge.

(Additional reporting by Ed Stoddard; Editing by James Macharia and Alison Williams)

By Ed Cropley and Tiisetso Motsoeneng