Thousands of postal voters in the parliamentary constituency of Bristol West have received papers intended for people in Bristol East.
All 2,378 affected voters have been sent a letter from Bristol City Council's electoral services.
Council chiefs advised people to tear up the incorrect ballot papers and said replacements would be sent out soon.
A spokesman urged people to send in the correct ballot papers once they received them.
He said the council would ensure none of the incorrect papers would be counted.
He added: "Replacement postal votes - for Bristol West - should arrive no later than 4 May. Every effort will be made to ensure delivery by 30 April.
"Completed postal votes can be posted back or handed in to the Council House or any polling station within the Bristol West constituency.
"The city council apologises for any inconvenience caused," the spokesman added.
• The candidates for Bristol West are: English Democrats: Jon Baker; Green: Ricky Knight; Independent; Danny Kushlick; UK Independence Party: Chris Lees; Labour: Paul Smith; Liberal Democrat: Stephen Williams; Conservative: Nick Yarker.