The Constitutional Court will rule on Thursday whether 181 ANC candidates, excluded in six municipalities because the party did not click "submit as final" on the IEC's online system, can contest next month's local government elections.
The court will hand down judgment at 10 am on what the law requires from parties that submit their party lists and ward lists electronically.
The elections take place on November 4.
The IEC excluded the ANC's candidates in Sundays River Valley, Walter Sisulu, Ngquza Hill and Port St Johns in the Eastern Cape, uMshwathi in KwaZulu-Natal and the Mangaung metro in the Free State.
The party had loaded its lists onto the IEC's online candidate nomination system and paid its deposits before the 5pm deadline on August 28, but did not click the final button that confirms the lists.
The IEC told the ANC on September 1 that the lists would not be accepted.
The Electoral Court upheld the IEC's decision last month and dismissed the ANC's appeal.
IEC deputy chief executive Masego Sheburi said this week the commission had drawn up contingency plans and would have to reprint a large share of the affected ballot papers if the court ruled in the ANC's favour.
Deputy chief justice Dunstan Mlambo reserved judgment after the court heard argument on Monday and said the decision would be delivered urgently.
Advocate Daniel Berger SC, for the ANC, told the court that clicking the button was not a step required by law and that the party's lists were already with the IEC before the deadline.
The ANC told the court it was not asking for condonation or an extension of the deadline, but for a declaration that its nominations had been validly submitted.
When asked from the bench how the IEC could tell a draft list from a final one, Berger said a lecturer would not refuse to mark an essay simply because it was handed in as a draft.
Advocate Terry Motau SC, for the IEC, conceded that the requirement to click the button was not expressly written into the act or its regulations.
He argued that the ANC could not attack the requirement after it had used other features of the online system that were also not set out in the regulations.
Motau said the ANC had not asked the courts to excuse its late compliance, and that any relief should be limited to the dispute between the IEC and the ANC.
The DA, which joined the case in the Electoral Court, backed the IEC.
Advocate Michael Bishop, for the DA, told the court that dozens of other parties and more than 2,000 candidates had also not clicked the button.
He said a ruling in the ANC's favour would have to apply equally to all of them, which would complicate ballot preparations and the holding of a free and fair election.
The ANC first blamed technical faults on the online system, but dropped that argument in the Electoral Court after the IEC showed it had no basis.
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