Catherine McCartney, who has been a strong campaigner since the death of her brother, has written to all TDs and senators outlining her concerns over Ms Cahill’s Seanad nomination and her involvement with the Republican Network for Unity (RNU) group.
She called on Ms Cahill to clarify her participation in the RNU and said the nomination has “grossly undermined victims of dissident republicans and the IRA”.
Ms McCartney, whose brother was murdered in Belfast in 2005, raised concerns over Ms Cahill’s “alleged senior position in RNU which, it appears, was as recent as 2011”.
A Labour spokesman last night said the party was proud to have Ms Cahill as their nominee.
He said: “Mairia Cahill has addressed her brief involvement with RNU on numerous occasions in the past and on the public record.”
Ms Cahill came to prominence when she spoke about her experience of being abused and the subsequent cover-up within Republican movement.
She is expected to be elected to the Seanad on Friday.
The Labour spokesman added that Ms Cahill is “fully committed” to the Good Friday Agreement, democracy, and the rule of law.
He said: “If elected to Seanad Eireann on Friday, she will use her position to promote these issues alongside her own priority area of youth unemployment and continuing to campaign on behalf of victims of abuse.
“The Labour Party is proud that she is our candidate in the bye-election.”
Ms McCartney yesterday told RTE’s Drivetime showsaid she decided to write to all members of the Oireachtas seeking answers.
“Questions were being asked and I thought very reasonable questions were being asked, and then it transpired that these questions were not being answered by Ms Cahill or the Labour party,” she said.
“Given my involvement in victim’s issues over the past 10 years I have questions and I would like answers to these question.”
She said Labour had “lost credibility” in selecting Ms Cahill and were doing so for purely political purposes.