Fiji's president, Ratu Josefa Iloilo, is due to make an appointment to the post of leader of the opposition next Tuesday.
Radio reports say the solicitor general, Nainendra Nand, has confirmed giving legal advice on the issue to the president this week.
The Labour Party leader says he doesn't want to be part of the government because an effective Opposition is crucial.
Mahendra Chaudhry made the comment amid debate over who is in the opposition and who will be opposition leader.
The prime minister, Laisenia Qarase, has said his understanding of the law is that with Labour now part of the cabinet, its backbenchers and their leader would be part of the government.
However, Mr Chaudhry says the law does not specify this and an effective Opposition is vital.
"In a democratic society you need an effective opposition, not just a token opposition. So we have decided in our caucus to play that role. In so far as our participation in the multi-party cabinet is concerned we are there as an entitled party on invitation, we are not a party in government."
But legal opinion generally is that as Labour is now part of the government, the only party left in the opposition is the United People's Party and its leader Mick Beddoes, or fellow UPP MP Bernadette Rounds Ganilau are the only people eligible for the post.
The official secretary to the president, Suliasi Turagabeci, says all the papers are being prepared for the appointment.
Reports say although an appointment is yet to be made, Mr Chaudhry is still occupying the parliamentary office of the rightful opposition leader and using official vehicle of the holder of the office.