There is still no date for a presidential run-off
Half of the results from Zimbabwe's parliamentary polls in March have been challenged in court, state media says.
Lawyers say the 105 petitions should not disrupt the work of parliament, but could in the end overturn the opposition's historic majority.
The announcement came as southern African mediators arrived for talks over the presidential run-off impasse.
The opposition might boycott a run-off, saying candidate Morgan Tsvangirai was the rightful winner in the first round.
Results published by Zimbabwe's electoral commission last week gave Movement for Democratic Change (MDC) leader Mr Tsvangirai more votes than President Robert Mugabe, but not the 50% needed to avoid a run-off.
The MDC says he won at least 50.3%.
Mr Mugabe has said he will stand in a run-off, but a date for the second round of voting has yet to be set.
The MDC says the official death toll of their supporters killed in post-election violence has risen to 25, but the party fears the figure could be higher.
The Southern African Development Community (Sadc) has been at the centre of efforts to resolve the deadlock in Zimbabwe following elections in March.
On Tuesday, African Union foreign ministers discussed the crisis in Zimbabwe.
AFP news agency reports that the body called for "a free, transparent, tolerant, and non-violent" run-off.
The ruling Zanu-PF party has filed petitions challenging the results in 53 constituencies and the MDC has challenged 52, Zimbabwe's Herald newspaper reports.
That is exactly half of Zimbabwe's 210 parliamentary seats.
The petitions were filed by losing candidates for alleged electoral malpractice like vote-buying, intimidation and corruption.
To cope with the extra legal work, the chief justice has appointed 17 more judges to hear the cases in the electoral court.
Under the law, the court has six months to deal with the cases, with another six months allowed for appeals.
But constitutional lawyers say the cases should not disrupt the work of the government and parliamentarians can still be sworn in.
There will be by-elections only if the electoral court declares the seats vacant.
Normally, the newly elected MPs would be sworn in within a week of the election, but because of the ongoing impasse over the presidential poll, there is still no indication of when that might be.
Meanwhile, the MDC says that five more of its supporters were beaten to death on Monday night by Zanu-PF supporters, bringing the number of MDC members killed in post-election violence to 25.
"We think the actual death toll is even higher because there are some farming areas that have been cordoned off by militias and vigilante groups," MDC spokesman Nelson Chamisa told AFP.
The BBC's Orla Guerin, reporting undercover in Zimbabwe, says there is a systematic attempt under way to change the political landscape.
She says the aim is electoral cleansing - to drive opposition supporters from their voting areas, or make them too afraid to vote for the MDC again.