The Government is being urged to declare a national emergency over the rail "crisis" amid warnings that stations are no longer safe and staff face growing abuse from angry passengers.
The Transport Salaried Staffs Association (TSSA) said ministers should convene an urgent meeting of the Cobra committee, claiming that delays to Govia Thameslink Railway (GTR) services are now the biggest rail breakdown in peacetime history.
The union said the latest new timetable introduced by GTR this week - the third since May 20 - is doing nothing to improve services or alleviate the "misery" of passengers and staff.
A survey of TSSA members at GTR showed that stations are no longer safe for staff because of rising levels of passenger anger at delays, said the union.
Nearly all of TSSA's GTR station staff have suffered abuse from passengers as a result of frustrations over cancelled trains, it said.
Most station staff said their jobs have become more difficult and their anxiety at work has increased since the new timetable changes came into effect.
Workers reported passengers being "treated like animals" and "forced into trains" that "clearly do not have the capacity to take them" because so many have been cancelled.
One station host said he had to help a season ticket-holder who was experiencing epileptic fits because of stress brought on by cancellations.
Union members reported that the situation had been made worse by the heatwave, with no toilet or water facilities made available on overcrowded platforms or trains.
TSSA general secretary Manuel Cortes said: "The breakdown in services at GTR is nothing short of a national scandal, but it is also a national emergency. Passengers are stranded at stations and squashed into trains.
"Overcrowding of carriages and platforms have escalated to seriously dangerous proportions for all concerned. Too many stations are no longer safe for passengers or staff and as workers can't make it to work so our economy is haemorrhaging money.
"Meanwhile, the Department for Transport has no grip on the situation and, given people are failing to be transported on their public rail service, it is hard to see how the DfT is fit for purpose.
"This week's new timetable changes have made no difference to the trauma facing passengers nor the abuse they are meting out in their frustration to staff. Our members are being turned into scapegoats."