A Papua New Guinea constitutional lawyer says there was no vacancy in the position of prime minister.
Yesterday, government MPs joined forces with the Opposition to have the prime minister's office declared vacant.
MPs then voted to make former treasurer, Peter O'Neill, the replacement for Sam Abal, who was acting prime minister in place of the ailing leader Sir Michael Somare.
The newspaper, The National, reports lawyer Peter Donigi saying that is outright illegality.
He says the move amounts to a vote of no confidence in the prime minister, and because it is within the 12 month period before elections, parliament should be dissolved and fresh elections called.
Mr Donigi says the opposition leader has no right to declare the office vacant.