Five senior judges found that elements of the referendum website and booklets were not "fair, equal and impartial".
It's a major blow for Children's Minister Frances Fitzgerald after it was reported that she played a key role in the drafting of the biased material.
It's emerged that the content for the website stemmed from a list of questions developed by the minister and another list of questions provided by a PR firm.
Transport Minister Leo Varadkar -- who was in charge of Fine Gael's campaign -- yesterday appeared to point the blame firmly at Ms Fitzgerald, adding that "nothing had gone wrong" from Fine Gael's side.
"This decision solely relates to the information campaign of the Department of Children," he said.
It doesn't relate to the Yes campaign run by Fine Gael and the Yes campaign run by all of the children's organisations," he added.
However a spokeswoman for Ms Fitzgerald today rejected that a spat has broken out between the ministers.
"Mr Varadkar has clearly said that the Government is taking collective responsibility for what has happened. To suggest that he is blaming the Children's Minister is wrong."
Last night Ms Fitzgerald defended the information used, adding that the Government had acted in good faith.