The row between the Rail, Maritime, and Transport Union (RMT) and Southern Rail has taken a new turn over revelalations that several stations are already unstaffed.
The dispute over conductor roles between the operator and the union has been ongoing, with industrial action planned over the Christmas period.
Now, the RMT has said that new parliamentary answers showed that 15 stations out of 156 are unstaffed on the routes the operator runs, while 58 are staffed for only part of the day.
Southern Rail maintains that changing the role of conductors to that of on-board supervisors will not diminish safety, pointing out that driver-only trains are in widespread use across the UK.
Meanwhile, the union insisted the figures revealed no official impact assessment of Southern's plans has been made, and warned this would "clearly disadvantage " passengers needing help.
RMT general secretary Mick Cash said: "Southern's basket case franchise and its relentless drive for profit at the expense of the safety of the travelling public and rail workers needs to be brought to an end.
"Dozens of stations have now been revealed to have no staff at all and many more are only staffed part of the time.
"The relentless drive to remove conductors as well from the trains and the company's refusal to sit down and settle the dispute shows the contempt that they hold for all concerned.
"Southern needs to be brought under public control so that safety and a service that everyone can access, not profit, is the main priority."