A first communication device generates respective media access control (MAC) protocol data units (MPDUs) that include respective data for a respective second communication devices, and determines respective resource units (RUs) via which at least some of the second communication devices are to transmit as part of an uplink (UL) orthogonal frequency division multiple access (OFDMA) physical layer (PHY) transmission to respectively acknowledge receipt of the respective MPDUs. The first communication device generates respective control frames that are configured to prompt the at least some of the second communication devices to transmit the UL OFDMA PHY transmission, and that include indicators of the RUs via which the at least some of the second communication devices are to transmit as part of the UL OFDMA PHY transmission. The first communication device generates and transmits a single multi user (MU) PHY data unit that includes i) the MPDUs, and ii) the control frames.