The biggest rail workers' union has set a deadline for taking its next step inthe long-running train guards dispute.
The Rail, Maritime and Transport (RMT) union has written to the new chiefexecutive of Southern Rail's owners Govia Thameslink Railway (GTR), Patrick Verwer, urging him to take an "early initiative" to resolve the row over the role of guards.
The union said it wanted a response by Thursday to allow its executive toconsider the company's position and make any decision on future industrial action.
The row over guards started on Southern more than two years ago, and has spread to four other rail operators, leading to a series of strikes which caused huge disruption to services.
RMT members on South Western Railway went on strike last Saturday and will walk out again on the next two Saturdays before a 48-hour stoppage at the end of the month.
The union recently reached a deal with Greater Anglia which it said guarantees a guard on trains.
RMT general secretary Mick Cash said: "RMT members have been fighting to defend the principle of a safe, secure and accessible railway for all on Southern Rail for well over two years.
The arrival of a new chief executive presents both sides with an opportunity to take a constructive approach and work on an agreement that matches the best practice in the industry in the wake of recent settlements including the deal on Greater Anglia."
Mr Cash said chaotic scenes at Brighton station on Saturday evening after the local Pride Festival, when thousands of passengers were kept outside the station, showed the need for a "properly staffed railway where safety and access comes first".