Zimbabwe's main opposition party CCC's spokesperson said the party has appealed the ruling at supreme court.
A Zimbabwe court on Thursday barred most opposition candidates from running in by-elections on Saturday that could take the ruling Zanu-PF party closer to changing the constitution.
The ruling is the latest twist in a battle for control of the opposition Citizens Coalition for Change (CCC) amidst heightened political tensions in the mineral-rich nation.
The Harare high court ruled in favour of Sengezo Tshabangu, whom the CCC leadership says is an impostor.
In October, claiming to be the party's interim secretary general, Tshabangu had the seats of 14 CCC lawmakers declared vacant by parliament.
This triggered by-elections in nine constituencies the CCC won under a first-past-the-post system in a disputed election in August.
The recalled MPs sought to win their seats back in the new votes scheduled for Saturday. Tshabangu argued that they could not run under the CCC banner without his approval and won in court.
A Harare judge ordered the names of eight of the nine lawmakers be struck off the ballot.
CCC spokesperson Promise Mkwananzi said the party has appealed the ruling at the Supreme Court.
Mkwananzi said the ruling showed "the kangaroo nature" of Zimbabwe courts and of the "total democratic regression" since President Emmerson Mnangagwa took office in 2017.
"The courts of Zimbabwe have ceased to be a just and neutral arbiter of disputes and that is worrying," he told AFP.
Zanu-PF victories in the by-elections would take it closer to the two-thirds parliamentary majority needed to amend the constitution.
Zanu-PF is currently 10 seats short of the supermajority in the 280-member parliament.
Analysts believe the party wants to remove a two-term presidential limit, and allow Mnangagwa, 81, to cement his control over the nation.
Critics have long accused Zanu-PF, which has been in power since independence in 1980, of using the courts to silence opposition lawmakers and dissent.
The case has sharpened political tensions that have been high in the southern African country since an August 23 vote that international observers said fell short of democratic standards.
The CCC, led by Nelson Chamisa, a 45-year-old lawyer and pastor, has complained about a campaign of intimidation against its members before and after the vote.
The party said one activist was abducted on Wednesday, the latest in a series of similar incidents in recent weeks that saw one CCC supporter killed and others snatched.
Chamisa has said Tshabangu is not a CCC member, the party has no secretary general, and has not expelled or recalled any MPs.
Tshabangu, who denies being a Zanu-PF stooge, is attempting to recall another 13 CCC lawmakers, and the case is currently in court.