The Solomon's government is in crisis following the resignation of six cabinet ministers and three backbenchers.
The group say they no longer have confidence in the leadership style of the Prime Minister, Manasseh Sogavare.
The move led by the reshuffled Finance Minister, Gordon Darcy Lilo, will now mean
the opposition can claim 28 members leaving the government with 13.
The Governor General has been requested to consider calling for an urgent meeting of Parliament within the next seven days.
The group want to submit a motion of no confidence if Mr Sogavare does not resign.
The leader of the Opposition and other members of Parliament have signed a Memorandum of Understanding to stay together to form a new government.
Local reports quote Mr Sogavare as saying he still has enough support in parliament and he will not step down.