Southern plans 60% service during five-day strike
Southern has promised to run 60% of its normal timetable if a five-day strike by the Rail, Maritime and Transport Workers union (RMT) goes ahead.
The two are embroiled in a long-running dispute over the role of guards, with talks due to begin on Wednesday.
Parent firm Govia Thameslink (GTR) asked Acas to mediate in an attempt to avert what the firm said was "damaging" and "unnecessary" strike action.
It has set a deadline of Thursday to avoid the strike schedule.
Southern services have been beset by delays and cancellations for weeks due to the dispute and staff shortages, which the company has blamed on high levels of sickness.
The RMT has offered to suspend the week-long strike - due to begin on Monday - if Southern puts its plans for guards on hold.
The plans involve new trains where the driver operates the doors using CCTV but the RMT fears job losses and has safety concerns.
It said the safety of the travelling public on "dangerously overcrowded trains and platforms" was "the fundamental issue at the heart of this dispute".
If the strike goes ahead, Southern said it would run a restricted service. Many routes would have fewer trains and some routes would have none at all.
However, it said with the use of "contingency" conductors it would run almost 60% of its normal timetable.
GTR passenger service director Angie Doll said: "We are sorry that our passengers once again look set to suffer further disruption because of the RMT."
She said the action was unnecessary as the plans would cost no-one their jobs and would free up staff on board trains to better serve passengers.
She also claimed the changes would lead to fewer cancellations in future.
"The new on-board supervisor will be able to go anywhere on our network, significantly reducing the perennial problem of train cancellations due to conductors not being available when they're delayed by disruption, for example," she said.
'Walk away from commitments'
At an evening rally in Brighton, Labour leader Jeremy Corbyn called for an end to Southern's franchise and repeated his party's commitment to return railways to public ownership.
He said: "They should have said, 'if you cut the services, we'll cut you out'. But that would take a government that stood up for people.
"What is the point of a franchise agreement … if a company can walk away from their commitments at no cost?"
When the strike dates were announced, rail minister Paul Maynard said RMT bosses were overlooking their impact on the travelling public and claimed GTR's changes would modernise services and be better for passengers .