PARENTS have launched a landmark legal bid to end Christianity's ruling role over religious studies in government schools.

Fairness in Religions in School believes "Sunday school lessons" by church volunteers should be replaced by "culturally diverse and unbiased" classes.

The group is challenging the Department of Education and Early Childhood Development in VCAT tomorrow in a hearing scheduled for seven days.

Three parents are expected to give evidence that their children suffered discrimination on religious grounds at government schools in Victoria.

The case has been supported by Australian Education Union Victoria president Mary Bluett, who said if it were successful it could revolutionise how religion was taught in schools.

"We support the intent of government schools being secular," Ms Bluett said.

But it could create demand for extra resources "and, of course, our primary schools do not have resources".

Parents' group spokesman Scott Hedges said the case did not oppose teaching Christianity in schools, but sought to ensure religious studies was culturally diverse and unbiased.

"We are parents who feel this hurts our children," Mr Hedges said. "The Government is allowing church volunteers to use the schools effectively to teach a Sunday school lesson.

"What we want is religion taught by teachers as cultural studies."

The Department of Education declined to comment on the VCAT case, but a spokeswoman said: "Students not attending special religious instruction are required to be engaged in positive, independent learning such as self-study, including revision, or activities such as peer mentoring, participating in clubs, or instruction in areas outside the core curriculum."

Holding Redlich partner Andrea Tsalamandris said her clients were not seeking damages and had a strong case because the children were segregated based on their religious beliefs.

Lyle Shelton, a spokesman for the Australian Christian Lobby, said the move defied Australia's cultural heritage.

"Religion has been taught in our schools for more than 100 years and as far as I know it hasn't done too much damage," he said.