A first communication device receives an uplink orthogonal frequency multiple access (OFDMA) transmission. The uplink OFDMA transmission includes respective transmissions from multiple second communication devices, and the respective transmissions from the multiple second communication devices include indications of respective acknowledgment policies corresponding to the respective transmissions from the multiple second communication devices. The first communication device generates one or more acknowledgment physical layer (PHY) data units to acknowledge at least a portion of the uplink OFDMA transmission, where the one or more acknowledgment PHY data units do not comply with at least one of the acknowledgment policies corresponding to the uplink OFDMA transmission. The first communication device transmits the one or more acknowledgment PHY data units to acknowledge the at least the portion of the uplink OFDMA transmission.