The South African Reserve Bank (SARB) should investigate whether certain banks, which had business relationships with the Indian Gupta family, were engaging in possible illegal activities, the opposition Democratic Alliance (DA) said Monday.

This came after certain banks such as the ABSA and First National Bank terminated their business relationships with Oakbay Investments and its subsidiaries, including Oakbay Resources and Energy, which are controlled by the Guptas.

However, these banks appear to have done so when the political weather changed: they only acted after the political fallout caused by Deputy Minister of Finance Mcebisi Jonas's public statement on March 16, claiming he had been offered the position of Minister of Finance by the Guptas, weeks before the firing of Minister of Finance Nhlanhla Nene on December 9 last year, the DA said.

"The sudden decision by certain banks to terminate their business relationships with the Guptas raises a serious question: did these banks comply with the relevant provisions of the Financial Intelligence Centre Act before the political fallout and their sudden decision to terminate their business relationships with the Guptas?" DA Shadow Minister of Finance David Maynier said.

The Financial Intelligence Centre Act requires banks to take reasonable steps to establish the source of funds, and to conduct enhanced monitoring of business relationships with politically exposed persons, their families and their closely associated persons.

The DA said banks could hardly claim not to have known about the political influence of the Guptas following the reported appointment of President Jacob Zuma's son, Duduzane Zuma, to the board of subsidiaries Oakbay Investments; and the publication of the official report of the investigation by the Justice, Crime Prevention and Security Cluster into the "culture of undue influence"by the Guptas.

The SARB is mandated to supervise and enforce banks compliance with the provisions of the Financial Intelligence Centre Act, Maynier said.

He said he has written to the SARB Governor Lesetja Kganyago, requesting him to order an investigation into whether certain banks, who had business relationships with the Guptas, complied with all the relevant provisions of the Financial Intelligence Centre Act, and if the investigation determines that certain banks failed to comply, to order any appropriate remedial action or administrative sanctions.

Allegedly with close ties with Zuma, the wealthy Gupta family has been under fire for exerting undue influence on Zuma's appointment of cabinet ministers. But the Guptas has denied the accusation, saying the have fallen victims to political struggle in the country.