The Electoral Office of Northern Ireland was threatened with legal action just 24 hours before the December 12 General Election after voters who tried to change address were removed from the register.
Solicitor Claire McKeegan of Phoenix Law issued pre-action proceedings against EONI in relation to a number of clients who were denied access to the register after being asked to provide documents they did not possess.
It comes as a whistleblower, who worked for EONI in the run up to the General Election, told the Nolan Show that they system was flawed, leaving hundreds of potential voters off the register.
The man, who was later dismissed from his job, claimed callers were told that the deadline to submit additional evidence, such as proof of address, was December 3 when the deadline was December 4 subsequently extended until the fifth.
He also claimed calls for queries across Northern Ireland were being taken on a single mobile phone, an old Nokia, which was being passed around between the staff.
The Electoral Office has refuted the allegations saying they "are not correct".
A spokesperson said staff worked tirelessly throughout the election period and that temporary staff were brought in to deal with an increased number of calls.
Ms McKeegan said her clients were eventually granted a vote but only after pre action proceedings were issued.
"One client was given less than two days to provide specific documents which she did not have have and simply could not obtain" the lawyer said.
"She was also informed that she has been removed from the electoral register for her family home.
"The application of these requirements discriminated in particular against young people who have recently moved out of the family home, and who do not have a mortgage but are renting their property", she added.
Ulster Unionist leader Steve Aiken said on Friday that the party is taking legal advice following the whistleblower allegations.
Tom Elliot stood for the UUP in Fermanagh South Tyrone, losing to Michelle Gildernew by just 57 votes, the constituency has been traditionally one of the hardest fought.
In 2010 Sinn Féin won with a majority of just four votes.
Mr Aiken said: "Confidence in the electoral system is absolutely essential. Fair and open elections are a basic right in any modern democracy.
"If the serious allegations from the whistle-blower are confirmed, then last weeks’ election was neither fair nor open for potentially thousands of voters across Northern Ireland.
"Allegations of members of the public being deliberately mislead over deadlines would be especially unforgivable if proven to be true.
“Even before these latest allegations came to light my party had serious concerns regarding the recent operation of the EONI and we had planned to pursue this directly with the organisation.
“The centralisation of the EONI to Belfast has been a total disaster. Phone lines were jammed, paperwork was going missing and clerical errors were common-place.
"We are currently taking legal advice in relation to what steps we may now take", he added.
