Papua New Guinea's deputy leader of the opposition, Mathew Siune, says he is expecting chaos in the Chimbu by-election which is to be held late in May.
Mr Siune says the Electoral Commission has not completed a clean-up of the rolls and many "ghost voters" remain on the lists.
The Electoral Commissioner, Andrew Trawen, has admitted that the rolls in five of the six Open electorates in Chimbu have not been cleaned.
He says this is because local councillors and other people have refused to assist the Commission in its work.
He says the Commission is ready for the worst during voting when officials continue their efforts to clean up the rolls by preventing voters trying to use the names of dead voters to cast illegal ballots.