There is but one law which, from its nature, needs unanimous consent. This is the social compact; for civil association is the most voluntary of all acts.
 Jean-Jacques Rousseau, The Social Contract (1762). copy citation

add
Author Jean-Jacques Rousseau
Source The Social Contract
Topic association law
Date 1762
Language English
Reference Of the Social Contract, or Principles of Political Law, Book IV
Note Translated by George Douglas Howard Cole
Weblink https://en.wikisource.org/wiki/The_Social_Contract/Book_IV

Context

“On these various considerations depend the rules by which the methods of counting votes and comparing opinions should be regulated, according as the general will is more or less easy to discover, and the State more or less in its decline.
There is but one law which, from its nature, needs unanimous consent. This is the social compact; for civil association is the most voluntary of all acts. Every man being born free and his own master, no one, under any pretext whatsoever, can make any man subject without his consent. To decide that the son of a slave is born a slave is to decide that he is not born a man.
source