Southern Railway has set a deadline for the biggest rail union to accept an offer aimed at averting strikes, or it will terminate conductors' contracts and press ahead with changes to their role.
The company, which is facing a series of fresh strikes by the Rail, Maritime and Transport (RMT) union from next week, issued the ultimatum as a "final attempt" to resolve the long-running dispute, which has caused travel chaos for months.
Southern said its new offer included a lump sum payment of £2,000 to conductors to be paid once the dispute is settled and its plans are fully implemented.
Its eight-point offer includes guarantees on conductors' jobs until 2021, above-inflation pay increases for the next two years and guaranteed levels of overtime.
In a letter to RMT leader Mick Cash, Southern said it will "regretfully proceed without the RMT's involvement" and serve notice letters to conductors, terminating their contracts and inviting them to sign up to the new on board supervisor role from January if it does not agree to the offer by midday on Thursday.
Govia Thameslink Railway (GTR), which owns Southern, has also invited the RMT to meet for urgent face-to-face talks, either directly or through the conciliation service Acas, to discuss the offer.
Charles Horton, chief executive of GTR, said: "Everyone is sick and tired of this pointless and unnecessary dispute and we now need to bring a swift end to these strikes which have caused months of misery for hundreds of thousands of workers, children going to school, family days out and retired people.
"We have a responsibility to the travelling public and our staff and, after 10 months of dispute, these strikes are plaguing people's lives and enough is enough.
"The union and conductors have had an incredibly fair and comprehensive offer on the table for nearly two months with job security for at least five years, pay increases and overtime guaranteed.
"Today we are going the extra mile and offering our conductors a lump sum cash payment to be paid just after Christmas when they are getting on with their new roles giving fantastic service to our customers.
"We've given the RMT and our striking conductors a fair, clear and unambiguous plan that we intend to implement if they won't do a deal. It's an incredibly reasonable offer and the union's arguments about safety and accessibility for disabled passengers are contrived.
"Independent experts have said that running trains with the driver closing the doors is safe and as a responsible operator we have always looked after customers with disabilities, and always will.
"The RMT needs to understand that this change is happening and we would prefer to work with them to ensure that it's achieved in a way that best protects the interests of our customers, our employees and the business.
"But no-one should be in any doubt that the deadlines are fixed and immutable and we will press ahead if there is no deal by Thursday lunchtime. This dispute has to stop, and stop now."