The contestation of global governance institutions can strengthen or weaken, as well as transform, them. This article analyses the productive potential of contestation and justification of global governance institutions by examining the multiple authorities that are invoked as auxiliaries in the process. It studies the (re-)construction of these authorities by dissecting authority into three components: power, legitimacy and connection to public interests. Empirically, the article focuses on the issue area of business and human rights, examining the highly contested process of drafting a binding instrument in the United Nations Treaty Process. The analysis shows that the success of the Treaty Process not only hinges on its direct reaction to contestation, but also on its ability to (re-)construct the multiple related authorities. Ultimately, the article argues that the contestation of global governance institutions involves (re-)constructing multiple authorities. This demonstrates how contestation can also affect global governance institutions, actors and norms beyond the specific field of deliberation.