Workers voted by 372 votes (51.8%) to 346 (48.2%) against the proposed deal
Members of the Aslef union have rejected a deal aimed at ending the long-running dispute over driver-only operated trains on Southern railway.
General secretary Mick Whelan said: “We understand and support the decision arrived at in a democratic vote.”
Mr Whelan said the drivers’ union would now “seek new talks and work to deliver a resolution in line with the expectations of members”.
Leader Mick Cash said the move reduced the safety of passengers and staff on board trains and urged Southern rail to put “safety before profits”.
Support is still growing for the rail workers’ actions, particularly since the massive increase in fares and further deterioration of the service.