One of the most glaringly unfair rules of Kira's village is that only boys and men are allowed to learn to read and write. No explanation is given for such an arbitrary and sexist practice. Another rule is that women cannot join men on the hunt. Although many women may not desire to go, and women have other duties of their own to perform, it doesn't seem fair to prevent a woman from going who might have skill in that activity.
Even more seriously unfair rules exist, however, and those affect the disabled or injured. Any child who is born with a congenital deformity is routinely left to die on the Field of Leaving; Kira only survived because her grandfather was powerful enough in the community to advocate for her. Even adults who sustain an injury that will cause permanent disability are sent to the field to die. Kira learns about Camilla, a woman who slipped on the rocks and broke her arm. Because her husband was unable to set the broken arm so that it would be usable again, Kira learns that "she'll probably go to the Field."
Other rules give the guardians the ability to control the society by means of deceit and murder. The guardians perpetuate the lie that beasts roam the forest outside the village, when, in fact, "there be no beasts." The guardians have killed off the parents of Thomas, Kira, and Jo in order to be able to use the children's artistic abilities to serve the community's needs. Guardians and artists live and work in the Council Edifice, the only place in town that has amenities such as running water. Compared to the squalor the rest of the citizens live in, especially those from the Fen, this lifestyle disparity is especially unjust.
Kira's society has many unjust rules, but the most egregious injustices apply to the disabled and injured as their right to life is stolen from them.