Australia's acting High Commissioner to Fiji is under orders to leave Fiji.
The Australian government says Sarah Roberts has been told by the Ministry for Foreign Affairs that she will be issued with a formal notice to leave the country.
Australia says the expulsion is linked to a postponement of a summit of the Melanesian Spearhead Group because of disquiet over Fiji's role as the new chair.
The group was formed to promote trade in the Pacific.
Australian Foreign Minister Stephen Smith says the decision is both unjustified and disappointing, but Australia will not retaliate.
Fiji also expelled Australia's High Commissioner last year.
Mr Smith has been a critic of Fiji's military regime led by Commodore Frank Bainimarama, which took power in December 2006.
Last month he attacked a decision by the government to limit foreign media ownership in the country to 10%.