The one-parent organisation One Family will today call for a constitutional amendment to reflect the changed nature of the family in modern Ireland.
The director of One Family (formerly Cherish), Ms Karen Kiernan, said the Constitution affords protection only to the family based on marriage. She will call for a "fundamental reform of family policy, including the existing legislative and constitutional framework, which do not reflect the changes in family structures that have taken place in Ireland and continue to take place."
One Family will be launched today as the new identity of what used to be Cherish.
Its call is being backed by a family law barrister, Mr Geoffrey Shannon, who says the State's reluctance to legislate in this area must be addressed urgently.
"The time is now ripe to consider changing the law to facilitate a broader and more inclusive definition of the family in a manner that will promote and foster the best interests of children. This may involve amending Article 41 of the Constitution," he added.
According to Article 41, the State "pledges itself to guard with special care the institution of marriage, on which the family is founded, and to protect it against attack".
Ms Kiernan said the nature of the Irish family has changed dramatically since 1937: "In the 2002 Census, almost 12 per cent of Irish households were headed by one parent, whether they were single parents, widowed person, separated or divorced."
She welcomed research published by the Minister for Social and Family Affairs last week, but said Ms Coughlan had to "grasp the nettle and ensure the State's policy recognises the myriad of family forms in Ireland today".