Opposition Movement for Democratic Change (MDC) leader Morgan Tsvangirai has vowed his party will not contest the November 26 polls. But his top lieutenants have rejected his calls, plunging the MDC into its worst crisis since its formation six years ago.
Analysts say the row will test Tsvangirai's power among his ranks and - whether the MDC survives it or not - considerably weaken Mugabe's only political opponents.
A faction supporting the MDC's participation in the senate polls, which critics say are meant to consolidate Mugabe's grip on power, said some candidates were preparing to register with provincial electoral courts closing at 1400 GMT on Monday.
But by mid-day, no MDC candidates had pitched up to register in the capital Harare, where Mugabe's ruling ZANU-PF party is contesting all the five seats at stake.
"I don't have details at the moment, but the information I am getting is that some candidates are getting ready to register and the process is going on well," said MDC national spokesman Paul Themba-Nyathi, a member of the pro-election group.
But Tsvangirai's spokesman William Bango said the pro-election faction was struggling to find volunteers to contest the senate polls, and might be forced to settle for some lower level candidates.
"The big guns, including some of those advocating that the party must participate in these elections, have quietly pulled out of the race because they realise their position does not enjoy popular support," he said.
The MDC leadership split almost in middle nearly two weeks ago over whether to participate in the polls for the senate, a new upper house of parliament.
Tsvangirai says he is using his authority as party leader to keep the MDC out of the senate elections as his party has nothing to gain from participating, but other MDC leaders fear a boycott will further edge the party out of national politics.