This year's general elections will be the first to be held in more than eight years.
"There is little confidence in the process at the moment," Anthony said in a statement to Radio Australia.
Felix Anthony is a former union leader elected as leader of his party Saturday.
Anthony added that the process governing the general elections -- the first after the bloodless military coup of 2006 that brought Frank Bainimarama to power -- is a disadvantage to the minority groups living on outer islands.
He also criticised the fact that the ballots force the voters to choose a number rather than a party or candidate directly by their name.
"What we are likely to see is a large number of invalid votes coming through," said Anthony, whose party promised to protect workers' rights.
Fiji passed a new constitution in 2013 and at the beginning of this year it established the Electoral Commission responsible for organising general elections.
Prime Minister Bainimarama transferred the leadership of the armed forces, a position which he occupied since 1999, in order to participate in the elections.
Fiji has a population of 800,000 inhabitants and since its independence in 1970 has experienced four coups due to unequal distribution of power between the Fijian community and the ethnic Indian community.
Ethnic Indians comprise 37 percent of Fiji's total population of around 870,000.
Most of them are descendants of indentured labourers who were brought in from India between 1879 and 1916 to work in the country's sugarcane plantations.