Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos) By the Chofetz Chaim

This book lists the Torah mitzvos that can be observed today

Second Section – the Negative Commandments

125. It is a negative commandment “do not have relations with one’s aunt as she is the wife of your father’s brother”

As it states in Vayikra (Leviticus) 18:14, “to his wife, you shall not approach, as she is your aunt.” This negative commandment is if she is the wife of your father’s brother from the father’s side. If the transgression happens during the lifetime of his uncle, both partners are given the death penalty of strangulation because she is a married woman. If it is done intentionally, after the death of his uncle, then they are spiritually excommunicated. If it is done by accident, then they are required to bring a sin offering. According to law of Shinus from the Sages, this law also applies to the wife of his father’s brother from his mother’s side and the wife of his mother’s brother from the father and mother’s side.

This applies in all places and at all times.