The Government has given an under-fire rail company permission to introduce an emergency timetable allowing them to cancel another 350 trains a day, it has been claimed.
The Rail, Maritime and Transport union said it was given the figures at a meeting with company officials from Govia Thameslink, which runs Southern Railway.
Southern services have been hit by a series of delays and cancellations for weeks because of a shortage of staff and strikes in a row over the role of conductors.
The company has blamed high levels of staff sickness for the daily travel chaos being suffered by passengers.
RMT general secretary Mick Cash said the emergency timetable will come into effect a week today, adding: "This latest savage attack on passenger services by GTR is nothing to do with staff sickness and everything to do with gross mismanagement of this franchise and the failure to employ enough guards and drivers to fill the current rosters and diagrams.
"The continuing attempt to blame the frontline workforce for this crisis is a cynical and cowardly ploy that will not wash with the travelling public.
"The solution of this failing, basket-case franchise is not axing more trains and attacking those trying to hold it together at the sharp end - it is the removal of Govia at the earliest possible point.
"Directly Operated Railways, who sorted out the mess on the East Coast, are lined up and ready to go and they should be given the green light to take over and start running these routes under public control, in the public interest."
The union and company officials will give evidence to MPs on the Transport Select Committee on Tuesday about the Southern chaos.
A GTR spokesman said: "We will be confirming details of a temporary timetable later this week. The timetable recognises that the present level of service has not been acceptable and will aim to give passengers a more predictable service they can plan around. This will be a temporary measure until train crew availability levels return to normal."
A Transport Department spokesman said: "We are clear that GTR passengers are not getting the service they deserve and the current situation is unacceptable.
"We are aware that GTR is considering some changes in order to strengthen their timetable in the face of ongoing disruption, so as many services as possible can run.
"When this happens, operators are contractually obliged to inform us in advance, but these decisions are taken only when there is no other solution, and this does not amount to the Government giving permission."