A network device receives multiple protocol data units (PDUs), or packets, and initiates aggregation of an intended number of the packets to form a transmission block. During the aggregation process, the device receives a priority PDU, or packet, and in response to receiving the priority PDU, terminates the aggregation process, either permanently or temporarily, even though the number of packets aggregated prior to receiving the priority packet is less than the number of packets intended to be included in the transmission block. The device releases the priority packet for transmission out of turn, ahead of the already aggregated packets. The priority packet can be released individually, with the aggregation being resumed after release of the priority packet, or the priority packet can be pre-pended to the already aggregated block of packets and the entire block released with a priority assigned according to the priority of the priority packet.