A government-initiated parliamentary inquiry into ethics classes advocated the approach in April, angering supporters who claimed it was designed to impede their take-up in schools.

The Education Minister, Adrian Piccoli, confirmed on Tuesday that ethics classes will be retained in NSW schools but said the government would introduce the new system. This means parents will be first offered a place in scripture classes and only told about ethics in a follow-up letter if they opt out.

The Greens MP John Kaye described the change as ''a massive road block'' to parents being informed of ethics classes.

''The government will now force schools to hide the existence of ethics classes,'' he said.

Dr Kaye accused the government of agreeing to the recommendation to keep its ''deal'' with the Christian Democrat MP Reverend Fred Nile, whose party shares the balance of power in the upper house.

''Nothing in the Education Act requires this level of discrimination against the ethics classes and their providers,'' he said.

''This is simply the O'Farrell government delivering on a deal with the Christian Democrats for their vote in the upper house.''