A multicast radio data communication system comprising a master and a plurality of slave stations uses a retransmission protocol. Data is transmitted by the master station and received by the slave stations. Slave stations having the weakest radio link are designated primary stations, and all other slaves are designated secondary stations. Any slave station may transmit a negative acknowledgement but only the primary stations may transmit a positive acknowledgement. Positive acknowledgements are transmitted in separate time slots, but negative acknowledgements transmitted by the secondary stations overlap the positive acknowledgements transmitted by primary stations. These negative acknowledgements corrupt reception of the positive acknowledgement by the master station, thereby ensuring that the data is retransmitted.