The Educate Together group, which oversees multi-denominational schools in Ireland, has said that last week's census figures on religion have serious implications for the State's education system.
"The fact that an increasing percentage of our population do not identify themselves with the traditional religious communities should ring alarm bells in the legal sections of various government departments," it said in a statement.
"The legal implications of the State continuing to sustain an overwhelming monopoly of schools obliged in law to uphold either one of the main religious communities are serious," it said.
It pointed out that "99 per cent of all national schools in Ireland are owned and controlled by either Catholic or Protestant Church authorities.
"This is leading an increasing minority of families to be compelled to send their children to schools that conflict (with) their lawful preference and conscience.
"This is specifically prohibited by Article 42 of the Constitution. It also runs counter to numerous international legal instruments to which Ireland is a signatory," it said.
The group drew attention to the census figures which show that the percentage of the population identifying themselves as Roman Catholic has declined to 88 per cent, its lowest level since census figures were first published in 1881.
It further noted that "the percentage professing 'no religion', plus those identifying themselves as atheists or agnostics, now exceeded those who identify themselves as Protestant.
"The relative percentages of children aged 0-4 to those aged more than 15 show a decline in the Catholic, Church of Ireland and all other segments except those for Methodists, Muslims, Orthodox Christians and those who do not wish to state a religious identity," it said, while the percentage of Catholic under-5s is three per cent less than that for the population as a whole.
"It is a growing necessity to develop a national network of schools that provide a legal guarantee of equal access and esteem to all children, irrespective of their religious backgrounds," it said.
"This will start to bring the structure of Irish primary education closer to the norm for a modern democratic State - of an inclusive State-owned and funded sector operating alongside specific denominational provision and in which all parents have choice and their rights respected."