Justice Kevin Cross intervened to stress that a Yes vote in the May 22 poll would only have specific implications.
Justice Cross said they would include giving same-sex couples constitutional protections which are not afforded by the present civil partnership arrangements.
The No campaign group Mothers and Fathers Matter responded by saying that while they accepted Justice Cross was impartial in the debate, they believed his views were wrong.
Justice Cross also told Newstalk radio a Yes vote would not impact on surrogacy laws.
The No side raised what they described as “serious concerns” over links between the organisation Atlantic Philanthropies — which has funded a number of groups on the Yes side — and the Government’s children’s agency, Tusla.
READ MORE: Marriage Equality Referendum: Voting yes is about ensuring fair play for all our children
Independent Senator Ronan Mullen questioned the foreign funding of Yes groups.
“It has also emerged that Atlantic Philanthropies gave US$8m to Tusla, the Child and Family Agency in April and within weeks of that donation the Government slashed funding to the Catholic marriage support agency Accord for its pre-marriage courses and we want to know whether all of these issues are connected,” he said.
Mr Mullen said he did not agree with foreign organisations funding political campaigns in Ireland.
Tusla said the Atlantic Philanthropies donation had been used for a specific programme.
The row came as Taoiseach Enda Kenny said the result of the referendum would be closer than polls predicted, but that he expected the Yes side to win.
Campaigning in Dublin for the Yes side, Fianna Fáil leader Micheál Martin said announcing funding cuts for the Catholic marriage guidance agency Accord was bad timing, but he did not think it was “revenge” for the church’s No stance.
Meanwhile, a 10 year-old girl attending No campaign event in Co Meath suffered an allergic reaction after eggs were among missiles thrown at those taking part.
The incident took place outside Navan shopping centre at 4.30pm, where No campaigners led by Paddy Manning were canvassing passers-by. He said Muireann DeClar was sitting on the side of an advertising truck bearing a No campaign advert when the event “was attacked by youths throwing missiles including eggs”.
“Muireann suffered a severe allergic reaction, and her life was only saved by the swift reactions of her mother, Aoife, who administered adrenalin at the scene,” he said. “Muireann has since been hospitalised, where her condition is believed to be stable.
“While the attackers had no way of knowing that Muireann had an allergy, they had every way of knowing that she was a child of about 10 years old.”