The brother of 2000 coup frontman, George Speight, claims the military-backed Fiji government is using race to justify December's takeover.
Former MP Samisoni Tikonisau made the comment after the interim cabinet met to discuss plans to return Fiji to democracy within three years.
The interim prime minister, Commodore Frank Bainimarama, says parts of the1997 constitution will be reviewed to eliminate separate race-based rolls and racially classified votes.
One of the authors of Fiji's constitution, Dr Brij Lal, says moves to amend the constitution are illegal because under the Westminster system, only an elected parliament has the authority to do this.
Mr Tikonisau, the MP for the Tailevu North Fijian seat, claims the bulk of Fijians won't wear constitutional changes outside of parliament.
"They're trying to use this race issue as a justification for the illegal overthrow of government. But in my view it's totally uncalled for at this point in time and best left to parliamentary processes."
He says the current system, which allows for 25 open, 23 Fijian and 19 Indian communal seats, provides added protection for indigenous people as traditional land owners.