The RMT union has called a deal agreed by its fellow union Aslef and Southern Rail to end the strikes which have crippled London and the south of England as a "shocking betrayal" of workers and passengers.
Aslef, which represents train drivers, and the RMT, which represents conductors and others workers on the network, had been in dispute with Southern's parent company, GTR Southern, over its plan to introduce driver-only trains.
Both unions argued that the move, which would see the removal of conductors and mean drivers were responsible for closing the doors themselves, was unsafe for passengers and would lead to job losses.
The dispute has meant months of misery for commuters after services are abruptly cancelled or delayed due to industrial action or staff shortages.
Now the end could be in sight after Aslef agreed a deal with GTR Southern where the company promised to improve safety in exchange for the union recommending the deal to its 1,000 drivers who will now vote on it.
But after seeing details of the deal, RMT General Secretary Mick Cash said it would lead to the destaffing of trains.
He said: "This so-called agreement is a shocking and historical betrayal presided over by the TUC of not only the conductor grade and drivers, but also passengers, including disabled passengers, who have lost the guarantee of a second member of staff on their trains.
"This abysmal document lists a whole host of areas where a a train can leave without a second member of staff that will leave both the driver and passengers exposed and vulnerable, and which also represents a thin end of the wedge that will lead to the de-staffing of trains."
Mick Whelan, general secretary of Aslef, said: "I am pleased that we have finally been able to reach an agreement with the company which reflects the concerns of train drivers.
"I believe this deal can deliver a safer and appropriately staffed railway for passengers on Southern rail and I will be recommending it to Aslef members."
Additional reporting by PA
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