ABSTRACT:This article provides a normative justification for unions. It discusses three arguments. The argument from consent justifies unions in some circumstances, but if the employer prefers to not bargain with unions, it may provide very little justification. The argument from contestability takes as its starting point the fact that employment contracts are incomplete contracts, where authority takes the place of complete contractual terms. This theory of contracts implies that consent to authority has been given under ignorance, and, therefore, that authority (...) cannot be justified by consent. Contestability is a mechanism that can handle this problem for consent theory. It demands transparency, channels for voice, and a forum where contestations can be evaluated. This idea can be implemented in firms in different ways, but the argument from the separation of powers implies that unions are uniquely suited to implement contestability, since they are organized outside of the employer’s domain of authority. (shrink)