The ANC said on Tuesday it had decided to "recall" Zuma, a euphemism for removing him from office, but gave him no firm deadline to resign, setting the stage for a potential fight to wrest him from power.
ANC Secretary General Ace Magashule said the party's national executive was split on when Zuma should step down, although the party expected him to respond to the order by Wednesday.
Finance Minister Malusi Gigaba told CNN late on Tuesday Zuma was expected to address the nation at 0800 GMT on Wednesday.
"We expect that tomorrow (Wednesday) he is going to do the right thing," Gigaba said.
Zuma's spokesman could not be reached for comment and there was no official confirmation from the presidency that the address would take place.
Zuma is already facing a no-confidence motion in parliament, brought by the opposition Economic Freedom Fighters and set for Feb. 22.
Zuma has been dogged by scandal since he became president in 2009. He is fighting the reinstatement of corruption charges, which were dismissed before he became president, over a 30 billion-rand ($2.52 billion) government arms deal arranged in the late 1990s.
South Africa's economy has stagnated during Zuma's tenure, with banks and mining companies reluctant to invest because of policy uncertainty and rampant corruption.
Zuma has been living on borrowed time since Deputy President Cyril Ramaphosa, a union leader and lawyer once tipped as Nelson Mandela's pick to take over the reins, was elected as head of the 106-year-old ANC in December.
Ramaphosa narrowly defeated Zuma's ex-wife and preferred successor, Nkosazana Dlamini-Zuma, in the leadership vote, forcing him to tread carefully in handling Zuma for fear of deepening rifts in the party a year before an election.
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