An efficient retransmission mechanism for use in consideration of uncertainty of resource availability on unlicensed carriers in a Licensed-Assisted Access scenario. Particularly, there is provided a method for data transmission at a first communications device operable in both a licensed spectrum and an unlicensed spectrum. The method comprises initially transmitting a data block on an unlicensed carrier of the unlicensed spectrum to a second communications device operable in both the licensed spectrum and the unlicensed spectrum and retransmitting the data block to the second communications device in response to receiving a negative acknowledgement from the second communications device. The method also comprises abandoning the retransmission under a predetermined condition associated with the unlicensed carrier. Correspondingly, there is also provided an apparatus for data transmission at a communications device operable in both a licensed spectrum and an unlicensed spectrum.