Many students in secondary schools are being forced to study religious education despite rules which state it is an optional subject, it has been claimed.
Religious education was introduced to the curriculum for secondary schools in 2000 to allow students to learn about a range of faiths and beliefs.
However, Atheist Ireland has gathered evidence which it says shows that many second-level schools are teaching religious education on a compulsory basis.
It claims that many of these schools are merging this State course with their own faith formation classes
John Hamill, of Atheist Ireland, said schools have placed a series of barriers in the way of students who wish to opt out of the subject.
“It’s easier to opt out of purgatory than it is to opt out of religion at second-level,” Mr Hamill said.
“Secular parents and those of minority faiths are being forced to have their children subject to Catholic faith formation as part of this State course.”
Mr Hamill said many parents are told that it is a core subject and any child who opts out will be forced to sit at the back of the classroom rather than being allowed to study another subject.
The campaign group has also obtained documents which it says show how the formation of the religious education subject in the mid- to late-1990s was heavily influenced by the Catholic church.
Records show that the department of education at the time warned that any part of a State course on religion would need to be scrupulously neutral or else it could breach articles of the Constitution.
However, Atheist Ireland claims that these new documents show the Catholic church played a key role in determining the content of the course.
In addition, it says non-Christian groups were excluded from the course committee established by the National Council for Curriculum and Assessment (NCCA) to advise on the content of the course.
Jane Donnelly, of Atheist Ireland, said the course discriminates against secular and minority faith families and called on the Minister for Education to issue a circular to schools advising them that the State's religious education subject is not compulsory.
She said students should be given the option of choosing another subject instead of religious education.
In response to queries, the NCCA said that while the Catholic church was represented on its course committee, it was as a provider of education and an education partner, along with many other groups.
A spokesman said there was extensive engagement with a number or religions and belief groups, such as humanists, evangelical churches and other minority faiths, during the formation of the course.
The NCCA spokesman said the subject is due to be reviewed as part of the reformed junior cycle, and this would be informed by the experience of students, teachers and patrons.
The council has previously pointed out that the subject is optional and parents have the right to withdraw their children from any subject that is “contrary to the conscience of the parent” under the Education Act.
It has said that students who find they have difficulty in opting out of a subject should raise it with their school’s board of management.