The parent-run lobby group, Fairness in Religions in Schools, has paid for a billboard attacking Special Religious Eduction classes in public schools, to be erected at a busy intersection in Liverpool on Monday.

A page from the Anglican SRE teaching materials.

Fairness in Religions in Schools chief executive Lara Wood said the billboard was in response to what the group sees as evangelism in public schools which they claim is poorly regulated by the NSW government.

"Scripture classes push messages about sin, death, suicide, sexuality and female submission onto children without the knowledge of their parents," she said.

"The Department of Education has no control over the program and it is time these classes were removed or at least regulated by the government."

A spokesman for the Department of Education said it works with scripture class providers to ensure the material is "sensitive, age appropriate and of a high standard."

A government audit of extra curricular prayer groups in public schools is also underway.

Anglican Archdeacon of the Central Coast, Rod Bower, well known for his signboards outside his Gosford church, said SRE classes should be replaced by a "a quality general religious education program" in public schools to reflect "this multicultural, multi-faith society."

"If parents want their children formed in a particular tradition they should take them to a place of worship," he said.

A billboard designed by the Fairness in Religions in Schools lobby group.

The government has hired an external consultant to review SRE and Special Education in Ethics in public schools. It is considering a controversial proposal to change the scripture class enrolment form which would remove the option to "opt out" of SRE in favour of asking parents to state the child's religion.

Greens education spokesman John Kaye said parents were becoming increasingly concerned about religious groups pushing "dangerous ideas" into public schools.

"This is the beginning of the backlash to an enrolment form that obscures the existence of the ethics alternative," he said.

"It is not surprising that community groups react by trying to warn parents about the messages their children might be exposed to in scripture classes."

The billboard quotes from an Anglican SRE text stating: "God says you are stuck in your sin and need to be rescued from his judgment."

Anglican Bishop of South Sydney and chairman of the Sydney diocese's SRE taskforce, Rob Forsyth, said scripture classes did not proselytise but provided education in Christian faith.

"If someone signs their kid up for education in the Christian faith, that's exactly what that kid should be taught," he said.

"If these parents don't like it, no one is forcing their child to attend SRE classes. They don't have to go. It's as simple as that. But they should not be trying to stop other people from sending their kids to SRE if that's their choice."