Up to 900 displaced Solomon Islanders could be deprived of the right to vote in Friday's South Guadalcanal by-election.
The voters, who fled to south Honiara during the reign of the former warlord Harold Keke, are ineligible to vote outside the constituency.
The chief electoral officer, John Babalu, says the law does not allow postal voting or a polling station to be set up outside the electorate.
"Their rights to cast a vote have been deprived because of this part of the provision that doesn't allow the returning officer to create a polling station outside of the constituency."
Mr Babalu says there are suggestions that one of the six candidates contesting the seat will charter a boat to allow them to take part.
The seat has been vacant for a year following the murder of its former MP, the late Father Augustine Geve.
The candidates are Rolland Seleso, Stephen Noel Ngele, Victor Totu, Josiah Karich, Sethual Kelly and Shadrach Sese.
South Guadalcanal has been the scene of brutal rivalries and in-fighting due to conflict sparked by Harold Keke.