Representatives of single-parent families have called for significant changes to the Constitution to provide such families with greater equality and legal recognition.
In a submission to the Oireachtas Committee on the Constitution, which is examining Articles 41 and 42, which deal with the family, the organisation One Family claimed that families headed by single parents or unmarried couples had little if any protection under the Constitution, compared with families headed by married parents.
One Family wants the current articles to be scrapped and replaced with clauses which put the interests of the child first, regardless of the marital position of the parents, and to place an obligation on the State to respect and support all forms of family life.
This meant that 12 per cent of all households, or 154,000 families, which are headed by single parents, did not have the same equality as families headed by a married couple, the group said.
Dr Fergus Ryan, a constitutional law expert and vice president of One Family, said that the current wording of the Constitution "simply does not countenance that there may be families situated outside the confines of the nuptial state".
He said that the Supreme Court had consistently found that the provisions of the Constitution relating to family applied only to families where the original adult members were married to each other.
This meant that cohabiting couples with children, along with widows, single and divorced fathers and mothers, had far fewer rights under the Constitution than married couples, One Family said.
According to Dr Ryan, while the Constitution has been interpreted to recognise the relationship between an unmarried mother and her child, there was no such recognition for unmarried fathers, and therefore they had fewer rights relating to their children when compared with married men.
The law assumes "that children with non-marital fathers somehow need his input less than those with marital fathers," said Dr Ryan.
One Family claimed the Constitution was also seriously flawed in that protection was accorded to married parents rather than their children. This "parent-centred" approach had meant the law was focused on the rights of the parent over the State, rather than on the best interests of the child.
"The result of this philosophy is a legal framework that views children simply as an adjunct of the family," Dr Ryan said.
"One Family believes that the Constitution should place children first, that in all cases concerning children their best interests should be paramount. Parental rights are too often placed to the fore of constitutional argument."