Human error caused a cash-strapped council to send the wrong letter out to 180,000 residents at a cost of £50,000, it has admitted.
Newcastle City Council wrote to electors last month to tell them about changes in how they register to vote but, due to a mistake, the wrong information was posted out.
People whose personal details were on the open electoral register received a letter intended for those not on the open register, and vice-versa.
A council spokesman said the wording of the two different letters they sent out was wrong, but the register was correct. He stressed there was no data protection issue and blamed human error for the wrong letters going to the two separate groups of voters.
Now the council has written again to all 180,000 voters, apologising for the mistake and this time using the correct wording for each group.
Council chief executive Pat Ritchie, speaking in her role as electoral registration officer, said: "We got it wrong and I would like to apologise for any confusion.
"I'd also like to reassure everyone that although the wording in the letter was wrong, the register is correct and no one's details have been compromised in any way."