Parliament's Speaker, Seoule Simeon, has ruled that Gracia Shadrack, MP for Malekula, should lose his seat for missing three consecutive sittings.
The Daily Post reports that Mr Shadrack, an Opposition MP, is to challenge the decision in court.
The Opposition claims that Mr Shadrack had been absent for medical reasons.
It claims that a letter explaining this was provided to parliamentary staff and should have reached the Speaker's office.
The declaration comes as the opposition pushes for Mr Simeon to stand aside while facing charges including assault and kidnapping - which he has denied
The Speaker was last month ordered to pay $US5000 in damages to a woman in a civil case over an incident in 2016.
The Opposition has boycotted this week's extraordinary sitting of Parliament in protest at the Speaker's refusal to step aside.