Education Secretary Michael Gove is being urged to publish guidance on how to broach the subject of abortion in schools following claims that groups campaigning against it are giving children false information.
Leading sexual health groups, teachers and student unions say the false claims are spreading alarm among children.
In their letter, the groups – which include the British Humanist Association, the National Union of Teachers and some Christian churches, say: "It is not the anti-abortion ideology that we are challenging.
"What prompts this letter are issues of fact: many of the claims these groups are making are simply false.
"For example, there is no evidence that abortion can increase the risk of breast cancer or infertility: no evidence that hormonal contraception can cause an abortion: no evidence for a medical condition called 'post-abortion trauma': or indexed that abortion causes more distress for women than carrying an unintended pregnancy to term."
The Society for the Protection of Unborn Children denied making false claims, insisting it said only that abortion may cause breast cancer.