A fresh row has broken out over the deadlocked Southern Railway dispute after the company was accused of refusing approaches for unconditional talks.
The Rail, Maritime and Transport union said the train operator had told the conciliation service Acas it was prepared to discuss only the implementation of its plans to change the role of conductors.
Southern insists it is prepared to meet the union to discuss its offer and has told the RMT it will press ahead with the changes if the union does not reach agreement by noon on Thursday.
It will "regretfully proceed" without the RMT'S involvement and serve letters to conductors terminating their contracts.
Southern made a final offer, including a payment of £2,000 to all conductors once the dispute was settled. The offer, which might be withdrawn after Thursday's deadline, was described as a bribe by the RMT.
The union repeated its belief that a deal was possible which matched a package agreed recently on ScotRail in a similar dispute.
RMT general secretary Mick Cash said: "The rejection of unconditional Acas talks by Southern confirms that they have no interest in a settlement and are hell bent on confrontation.
"In more than three decades as a union official I have never encountered such a shocking attitude to the basic principles of industrial relations.
"RMT is fighting to protect safety and access to services. It's time for the Government to get off the fence and to tell their contractors to get the gun away from the guards' heads and to start talking seriously about a deal that is there to be done.
"If it's good enough for ScotRail, it's good enough for Southern."
The RMT is planning a series of strikes from next week.