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
First Section – the Positive Commandments
50. It is a positive commandment to honor a Cohen (priest)
As it states in Vayikra (Leviticus) 21:8, "And you shall make him holy." This means you shall make him holy and prepare him so he is fitting to bring karbanos (offerings). Also, you shall treat him with honor and give him precedence in all matters: he is called up first to the Torah reading, he makes the blessing first at a meal, he is given a nice portion first. We are required to honor him even if he refuses the honor as it states, "And you shall make him holy," even against his will. Even if the Cohen has a deficiency that makes him unable to perform the services, we are required to honor him.
This is required in all places and at all times, for men and for women.