The acting director of the Pro-Democracy Movement in Tonga says the move to include two Peoples' and two Nobles' Representatives in the next cabinet is unconstitutional.
The proposal was made by the Royal Family earlier this month.
The Reverend Simote Vea says the Parliament would need to be called before the March elections if the move was to be implemented in time.
The Reverend Vea says as it stands the proposal cannot go ahead.
"There has to be a parliamentary passing of a change in Constitution before any form of change can take place. When the announcement came, it came when the parliament was closed and they said they were going have it before the election next year. Definitely there has to be some change in the Constitution or law before it can be active."
Parliament is not expected to meet until May.