Opposition leader Sam Rainsy said Wednesday the ruling Cambodian People's Party has deleted thousands of names from voter lists under a pretext of cleaning them up.
Voters who support the opposition are being wiped from the lists, he said.
The lists will be an essential part of voting across the country when Cambodians vote for national leaders in July 2008.
CPP officials could not be reached for comment Wednesday.
With deletions of opposition voters, the CPP will not have a competitive party to contend with "and we know the result of the election right now," Sam Rainsy said.
Commune elections held earlier this year saw remarkably low voter turn-out, and small parties complained the process had been tainted and complicated for opposition supporters.
Koul Panha, director of the independent Committee for Free and Fair Elections, said his monitoring group found voting irregularities in 160 of Cambodia's 1,621 communes following the elections. These would likely affect the outcome of the national elections too, he said.