An access point (AP) may prioritize the allocation of uplink resources between multiple basic service sets (BSSs). In some aspects, the AP may select one of a plurality of BSSs, may allocate one or more random-access resource units (RUs) to only the selected BSS, and may transmit, for each of the selected BSSs, a respective frame indicating the random-access RUs allocated to that BSS. Wireless devices belonging to the selected BSS may contend for access to the random-access RUs allocated by the frame, and then transmit uplink data using the random-access RUs.