The Abortion Law Reform Association is calling on MPs to support the rights of women in a court battle it says is aimed at ending access to safe abortions.
The Court of Appeal will on Tuesday hear an appeal by the Abortion Supervisory Committee against a High Court ruling last year.
The ruling, by Justice Miller, questioned the lawfulness of abortions granted on mental health grounds, which are 98% of all those carried out.
Abortion Law Reform Association president Margaret Sparrow says the group Right to Life, which opposes abortion, is cross-appealing to ban all abortions, by arguing embryos should be given full human rights.
But she says the law needs to change to give women full reproductive rights, and such decisions should be made by Parliament, not the courts.
The Women's National Abortion Action Campaign says Right to Life has spent $86,000 on its crusade and is calling on the group to reveal its financial backers.