Members of the ANC have pushed for the president to step down as have alliance partners trade union federation Cosatu and the South African Communist Party (SACP).
Zuma has denied wrongdoing.
With campaigning yet to start, Zuma has openly backed former African Union president Nkosazana Dlamini-Zuma, to whom he had once been married, while Cosatu and the SACP have voiced support for deputy-president Cyril Ramaphosa.
The SACP at the weekend said it was mulling contesting the next general election on its own - a first for the party, whose leaders have been included in ANC-led cabinets since the end of white minority rule in 1994.