Blockchain technology has emerged as a promising infrastructure for enabling collaboration between mutually distrustful organizations. The enactment of blockchain-based collaborative processes typically requires a profound understanding of the process being executed, limiting support for flexible processes that cannot be fully prespecified at design time. To overcome this limitation, support for looseness, dealing with the configuration and execution of underspecified processes, is essential. In this paper, we conduct a systematic literature review to examine looseness support for blockchain-based collaborative processes from a behavioral and organizational perspective. In addition, we identify open research challenges to pave the way for further research in this area.