Amnesty International has urged Iran to drop from its penal code the punishment of death by stoning, a fate awaiting 11 convicted criminals, the group says.
Iran has some of the world's highest execution rates
Stoning to death is a "horrific practice, designed to increase the suffering" of those condemned, the UK-based rights group says in a report.
Three people are said to have been stoned for adultery, a crime in Iran, since 2002, despite a moratorium.
The majority sentenced to death by stoning are women, Amnesty says.
Campaigners against the death penalty say execution by stoning is particularly harsh - Iran's penal code stipulates the stones used must be large enough to cause the condemned pain, but not sufficient to kill immediately.
Amnesty's statement highlights the case of condemned woman Mokarrameh Ebrahimi.
The father of her children, both of whom were born outside wedlock, was stoned to death in July 2007.
Jafar Kiani was executed despite, five years earlier, the head of Iran's judiciary reportedly issuing a moratorium on executions by stoning.
Amnesty says Ms Ebrahimi and eight other women and two men face a similar fate to Mr Kiani.
The majority of those sentenced to death by stoning are women, who suffer disproportionately from such punishment, Amnesty says.
It says they are not treated equally before the law and are particularly vulnerable to unfair trials because they are more likely to be illiterate and therefore sign confessions to crimes they did not commit.
One of the eight women currently facing execution was allegedly forced into prostitution by an abusive husband who was a heroin addict, Amnesty says.
She was sentenced to eight years' imprisonment for being an accomplice to the murder of her husband - by one of her clients - and to death by stoning for adultery.
"Execution by stoning is a grotesque and unacceptable penalty which the Iranian authorities should abolish immediately," Amnesty International UK director Kate Allen said.
She also urged an end to the practice of executing anyone for committing adultery.
Amnesty says anti-stoning campaigners in Iran have managed to save some potential victims but they face harassment by the police and arrest for public order and security offences.
According to the law, men are buried up to their waists and women up to their breasts before being pelted with stones until they die.
Iran applies a strict interpretation of Islamic law. Although stoning is not prescribed in the Koran, some scholars say it is in the traditions of the Prophet Muhammad.