The Tasmanian Electoral Commission has been forced to discount 163 votes after a letter opening machine damaged thousands of ballot papers.
Electoral Commissioner Julian Type said in a statement that 2338 postal votes had been damaged because of improper operation of the machine.
The damaged votes were in the southern electorate of Denison where the fifth seat is expected to go down to the wire.
However, the result is unlikely to be affected by the blunder as Mr Type said the 163 votes destroyed would disproportionately affect Liberal candidates who are not in contention.
While 2175 ballot papers were repaired, 163 were unreadable and will be treated as informal.
''As Electoral Commissioner I bear ultimate responsibility for this extensive procedural failure, and I apologise unreservedly to Denison candidates and voters,'' Mr Type said.