A council has apologised to residents near Bristol after personal details were posted to the wrong households.
Bath and North East Somerset Council sent out electoral registration forms to people living in the BS39 postcode area, revealing information about other residents.
It said the "wrong details" were due to a "printing error" and steps were being taken to "put this right".
The Information Commissioner's Office (ICO) said it will be making inquiries.
The household enquiry forms were sent out last week to a number of addresses in the BS39 area, south of Bristol, by the council's Electoral Registration Office.
Despite being posted to the correct addresses, it was revealed on Monday the forms had been printed with the names, addresses, nationalities and age brackets of other households.
In a statement, the council's registration officer Maria Lucas said it had received a number of calls from people saying the "details on page two did not match their address".
"I would like to apologise to all residents affected and reassure them that steps are being taken to put this right and that their data on the register, cannot be accessed by anyone else," she said.
"This was a machine error and we are currently printing new forms which we will get out to people in the areas affected by the printing issue this week."
The council added that following the error, residents in the whole of BS39 postcode area would not be able to register electronically, as all security codes used for the electronic registration methods had been "blocked as soon as the issue came to light".
A spokesman for the ICO, said it had been made aware of the incident and would be "making inquiries".
"Organisations have a legal duty to ensure the accuracy and security of any personal data they hold," he said.