The southern African nation was due to hold nine by-elections on Saturday, but most opposition candidates were taken off electoral lists by courts in a chaotic runup to the vote.
President Emmerson Mnangagwa's party, ZANU-PF, is just 10 seats away from securing a two-thirds majority in parliament that would allow it to change the constitution.
"The ill fated by-elections are a sham," the main opposition party, the Citizens Coalition for Change, CCC, said in a statement on Sunday, describing it as "a judicial coup" and "an undeniable affront against the constitution of Zimbabwe."
"Accordingly, we will be filing a formal complaint to the judicial service commission," it said.
A nationwide election in August saw the 81-year-old Mnangagwa seal a new term and his ZANU-PF secure 177 of the 280 national assembly seats, with the CCC taking 104.
But two months later, 14 CCC lawmakers were kicked out of parliament and nine by-elections ordered. The other five seats are decided by proportional representation.
An obscure political figure, Sengezo Tshabangu, declared himself the CCC's "interim secretary general" and said that the 14 were no longer party members and could not keep their seats.
CCC leader Nelson Chamisa, a former preacher, protested that Tshabangu was not a party member and that no expulsions had been agreed.
But the parliament speaker from ZANU-PF still ordered new elections.
Courts ruled last week, confirmed by the Harare High Court on Saturday, that the opposition candidates could not stand again in their old seats.
The CCC has accused ZANU-PF of using Tshabangu in a "nefarious" campaign to remove opposition candidates from ballot papers. The ruling party has denied any role in Tshabangu's activities.
Results of the vote are due to be announced in the coming days.
Observers say ZANU-PF wants to scrap a limit on presidents serving more than two terms, that would allow 81-year-old Mnangagwa to extend his rule.
Mnangagwa came to power on the back of a 2017 coup that toppled the country's longtime ruler Robert Mugabe.