The Islamic State has issued a fatwa on when “owners” of enslaved women can have sex with them. The militant group claimed the move is an attempt to curb violations in the treatment of women they capture, Reuters reported. According to an IS scholar, the group is trying to justify the sexual slavery of women with this ruling.

The fatwa bars a father and son from having sex with the same female slave, and also does not permit the owner of a mother and daughter to have sex with both. The fatwa was found among several documents seized by the United States Special Operations Forces during a raid in Syria in May.

The terror group has been accused by the United Nations and human rights groups of abducting and raping thousands of women and girls, with many of them given to fighters as a reward or sold as sex slaves. IS has gloated over the existence of the practice and has also set up a department of “war spoils” to manage slavery.