Northern Ireland's Electoral Office has been accused of "unacceptable" failings over letters with false deadline dates for registration it sent out ahead of last year's general election.
The BBC's The Nolan Show spoke to one woman who said she, her husband and her son were unable to vote because they were told the deadline to submit additional evidence for their registration was November 26.
The actual deadline was December 4.
Sinn Féin MP Francie Molloy said: "These latest revelations raise further and very serious questions about the Electoral Office's handling of the voter registration process.
"The reality is that people have lost their democratic right to vote as a result of being denied the opportunity to register.
"This goes way beyond human error and is totally unacceptable."
Chief electoral officer Virginia McVea has said many of the issues raised were "inaccurate and unfounded".
"However, we have made it clear that given we dealt with hundreds of thousands of documents during this election in a very short period of time, mistakes are inevitable due to human error.
"We apologise to the people affected unreservedly.
"Most importantly, we advised on a number of occasions that these made no material difference to the outcome of the election."
The Electoral Commission, which oversees the administration of elections, has said it is not investigating the Electoral Office or gathering evidence against it, that the election was lawfully run and that it has seen no evidence of any systemic failure.
Mr Molloy said: "We have been consistently raising concern about the Electoral Office's capacity following their decision to close down regional offices."
He added: "There doesn't appear to be any effective scrutiny or accountability mechanism in relation to the Electoral Office.
"This is very concerning and totally unacceptable."
