We are first introduced to the Council of Guardians in Chapter Three of this excellent dystopian novel. It is clear from the respect and deference that is shown to the Guardians by both Vandara and by Kira that the Guardians are given an incredibly important place in the society in which this story is set. As it becomes clear as Kira's trial begins, they have the authority to grant life and death. Note what the chief guardian says to Kira:
"One of us will defend you using our greater wisdom and experience. Take a moment to think about this, because your life may depend upon it, Kira."
It becomes clear that the Council of Guardians are able to control the people because of the power and importance that the people give them. It is the Guardians themselves who are charged with making wise decisions on behalf of all the people, which can often result in having to decree the death of people like Kira who perhaps cannot contribute meaningfully to the society of which she is a part.