But the department says McDowell last considered the clause in 2004 and decided "it should not be amended". It added that the constitution guarantees religious denominations the right to manage their own affairs and this includes the right to recruit teachers committed to their school's religious ethos.

The Employment Equality Act outlaws discrimination against employees on nine grounds, including religion.

But a clause was inserted in 1998 allowing schools with a religious ethos to discriminate in the hiring and firing of teachers if they could show the teacher was undermining the school's ethos.

Undermining the religious ethos has never been properly defined and the INTO fears schools could sack a teacher over lifestyle factors.

In the early 1980s, Eileen Flynn was sacked by the Sisters of the Holy Faith in New Ross after she moved in with a married man and had a child with him. Flynn's dismissal was upheld in the High Court when the judge said it was reasonable that "Roman Catholic teachers should conform to the religious tenets taught in a Roman Catholic school".