text: The firm's parent company, GTR, has said an offer, which includes a Â£2,000 bonus, "cannot be available indefinitely" if strikes continue.
  But RMT bosses said the union had already rejected the offer, and accused Southern of using "threats and bullying".
  A two-day strike is scheduled to begin on Friday.
  The latest twist in the dispute comes as Southern reinstated a full timetable after three months of reduced services.
  An increasingly bitter dispute has caused months of disruption for passengers, as RMT members staged a series of strikes in protest at GTR's plans to change the role of conductors on Southern services in South East England.
  Rail chiefs made a "full and comprehensive offer" to the RMT on 3 October in an attempt to settle the impasse over the proposed operation of driver-only trains on the network.
  But in a letter to RMT general secretary Mick Cash, GTR said: "Should your next planned action proceed... the offer is withdrawn in its entirety and will no longer be available for the RMT to accept."
  Mr Cash said in a statement: "This is just more threats and bullying from Southern rail and does nothing at all to resolve the current safety dispute.
  "It's also completely meaningless as the union has already rejected the Â£2,000 bribe to sell out safety, and the company are well aware of that."
  At the height of the dispute, in July, Southern introduced a temporary timetable to help cope with staff absences, which compounded the problems caused by the strikes.
  The standard service was reintroduced on Monday, although it got off to a difficult start due to a broken-down train at Crawley, while trains between Eastbourne and Hastings were hit by a signal problem.
  A further three blocks of strikes are planned before Christmas.
target: Southern Rail's latest attempt to stop strikes on its network has been branded "meaningless" by union bosses.