The Pan Africanist Congress of Azania (PAC) wants the much-awaited motion of no-confidence against President Jacob Zuma set for Tuesday postponed because its expelled member of parliament is yet to be replaced.
The party wrote to the speaker of the National Assembly requesting to replace its leader Luthando Mbinda three weeks ago.
Mr Mbinda is PAC's only legislator and was expelled in June for alleged misconduct.
"We are warning Parliament as well as Speaker Baleka Mbete that if she allows the seating to proceed then such convention would be deemed illegal, unconstitutional as well as null and void. We have written a letter to replace a Member of Parliament but there have been unnecessary delay tactics from the officials. Our reason for postponement is that we do not have a representative," reads a statement from the party.
The party made it clear it does not intend to abstain from participating in the motion of no-confidence.
There had been reports that following Mr Mbinda's expulsion, the party will not be represented on Tuesday when MPs vote in the motion against President Zuma.
"PAC was voted into parliament by citizens and we have a constitutional mandate to execute. How can we abstain in such an important gathering that decides the fate of our people? We will definitely participate because if you abstain from participating then it simply means we are as well abstaining from the challenges that our people face in their daily lives," the statement reads.
The party said it would seek legal means if its request is not granted.
"We are left with no choice but to consult with our legal team to device other ways of forcing parliament to respond to our request. There is a syndrome of punishing the PAC every time we want to replace a Member of Parliament; we are always settling such matters in courts and we have been vindicated every time we come out of courts."
Meanwhile, Ms Mbete is expected to announce on Monday afternoon whether a secret ballot will be allowed in Tuesday's no-confidence vote.
Ms Mbete has been attacked by opposition parties for delaying her decision until the last minute.
The opposition says a secret ballot would encourage MPs of the ruling African National Congress (ANC) to vote in favour of removing President Zuma from office.
The Economic Freedom Fighters has threatened the House Speaker with court action if she does not allow a secret ballot.
But the ANC has warned that any of its MPs who support the no-confidence motion against President Zuma risk disciplinary action.