To enable a number of emerging applications, efforts from industry and academia have started to focus on defining 6G systems, in which more stringent requirements than those imposed on 5G systems are being considered. In particular, some 6G applications may require extremely low-latency on the order of 0.1ms, through which practical designs of channel coding can be investigated based on Finite-Blocklength Coding (FBC). In this paper, we focus on a joint FBC scheme over multi-user downlinks in the Industrial Internet of Things (IIoT), in which only several symbol durations are available for users within a requirement of extremely low-latency. Since a higher coding rate is obtained by enlarging the blocklength of FBC, we jointly encode users’ data bits over their allocated resources, through which an enlarged blocklength is attained. Specifically, we first formulate the multi-user joint encoding design with a matrix-based method. Then, we present the optimal power-constrained throughput within the extremely low-latency requirement by formulating a nonlinear bipartite matching problem. We finally demonstrate the benefit resulting from the joint FBC in terms of each user’s maximum obtainable distance. With the distance to each user varying, we also perform an analysis of the variation of the optimal power-constrained throughput.