A rail executive has admitted that an "absolutely shocking" advertising campaign urging passengers to contact the union at the centre of a bitter dispute over changes to the role of conductors was a mistake.
The move by Southern Railway led to a flurry of complaints by its passengers against the company rather than the Rail, Maritime and Transport union, which has been taking industrial action for months in protest at the controversial changes.
Alex Foulds, deputy chief operating officer of Govia Thameslink Railway, which owns Southern, faced criticism over the adverts when he was questioned by councillors in the London Borough of Lambeth.
Ed Davie said he could not believe the company would spend tens of thousands of pounds on newspaper adverts calling on its customers to attack the union, describing it as "absolutely shocking".
Mr Foulds said the adverts were a "mistake", adding that the RMT had also made mistakes, describing the current climate as "very tense",
He apologised for the level of service being provided by Southern, whose services have been delayed, disrupted or cancelled for months because of the industrial action, staff shortages and other problems.
He conceded that Southern was the worst-performing train operator in the country "by some distance".
Mr Foulds told councillors there had been a "considerable" rise in sickness among staff, while less overtime was being worked, adding: "This has made it very difficult to run a reliable service."
Jennifer Brathwaite, Lambeth Cabinet member for environment and transport, said later: "The service provided by Southern is nothing short of scandalous. Lambeth's residents are completely fed up with cancelled and delayed trains on a seemingly daily basis and we have been calling for the franchise to be taken over by Transport for London for a long time.
"London's Mayor agrees, as does nearly every other local authority affected by Southern's abysmal service, so we need the Government to stop dragging its feet and put in place a clear plan for this franchise to be transferred as soon as possible.
"The advertising campaign from Southern, which effectively attacked their own staff members and cynically attempted to bully the RMT, was extremely poorly judged and I'm afraid symptomatic of the shambolic way this franchise has been managed for years."
Ms Brathwaite has co-signed a cross-party letter to the Secretary of State for Transport, with representatives from Southwark, Lewisham, Croydon, Merton and Sutton Councils, asking for the immediate transfer of Southern's rail franchise to TfL.
RMT members will stage another 48-hour strike from Tuesday, with further stoppages planned next month, including just before Christmas, and over the new year.
Members of the drivers' union Aslef on Southern are currently voting on whether to go on strike in a row over driver-only trains.
Southern said it will run more trains during this week's strike, with 62% of the normal timetable operating.
Passenger services director Angie Doll said: "We are doing everything we can to provide as many services for our passengers as possible and I'm pleased that we're able to add more services this time to help passengers get where they need to go.
"We're sorry that once again our passengers are facing disruption through unnecessary industrial action. Over 99% of affected conductors have now signed up to the new role, which makes this strike even more pointless."
Southern said there will be no train services on some routes, with some stations closed during the action.