The call for resignation comes amidst corruption allegations against Zuma and social and economic issues [WP report] such as unemployment, economic stagnation and water shortages. The president had previously agreed to resign offering time frames ranging from three to six months, but the National Executive Committee (NEC) of the ANC has called for an immediate resignation saying, "While appreciating President Zuma's proposal, the NEC noted that South Africa is going through a period of uncertainty and anxiety as a result of the unresolved matter of transition."
The ANC invoked Rule 22.214.171.124 of the ANC Constitution [text] allowing the National Executive Committee of the ANC to recall any public representative. If Zuma does not step down, the issue could move to Parliament where a vote of no confidence would force Zuma and his cabinet to resign, empowering the parliamentary speaker as the acting president.
The ANC emphasized in their statement the need for a quick resolution in order to restore faith in the country's public institutions, stabilize the political climate and address the serious issues facing the economy.