The dispute on Southern Railways about whether drivers or on-board guards should close the train doors has dragged on for months, and commuters have complained that some have lost their jobs in the ongoing chaos.
Drivers joined the picket lines Tuesday, ensuring all Southern's 2,242 weekday services were cancelled.
Transport Secretary Chris Grayling blamed the unions and urged talks. Unions attacked the government, saying the issue is one of safety and that ministers have been preventing Southern from negotiating properly.