Talks aimed at avoiding a series of strikes in a row over driver-only trains have failed.
Rail operator ScotRail and the Rail, Maritime and Transport (RMT) union met at conciliation service Acas on Monday morning following a war of words in which the union accused the rail operator of "sabotaging" planned peace talks.
Phil Verster, managing director of ScotRail Alliance, said the claims were a "mystery" to him and accused the RMT of building their strike campaign on "misinformation".
Following the 11am meeting, an Acas spokesman confirmed the talks had been "adjourned with no date set to resume".
Read more: ScotRail denies 'sabotaging' talks to resolve driver-only trains row
RMT general secretary Mick Cash said: "ScotRail have no intention of engaging in serious talks.
"This morning, they set up a series of a serious of ludicrous preconditions that they know cannot be met by the union and, as a consequence, yet again they effectively sabotaged the process.
"The action remains firmly on."
Mr Verster said: "This strike is totally needless. The RMT have refused point-blank to talk to us about how we modernise and improve Scotland's railway.
"Instead, they have hidden behind a national policy that says that nothing must ever change.
"Tens of thousands of our customers will be disrupted and hundreds of our own people will be hit financially as a result of their intransigence.
"The public will be astonished to hear that this is a strike only about who opens and closes doors on trains, nothing more.
"The RMT are being, at best, disingenuous when they tell people that we are trying to have driver-only trains. We are not.
"We will still schedule a second person on-board when we bring in the amazing new faster, longer, greener electric trains from next year.
"Each and every day, people in Scotland make around 150,000 journeys on trains that have the doors safely opened and closed by the driver while a second member of staff carries out customer service duties. The RMT are hiding behind a safety argument that doesn't add up."
Earlier, the RMT protested outside ScotRail's offices with supporters holding RMT flags and banners reading "keep the guard on the train".
RMT regional organiser for Scotland Mick Hogg said: "If, God forbid, there was a collision or a derailment there would be no-one who is safety trained in order to evacuate the passengers safely. The guard's role is a safety-critical role."
Rail regulator the Office of Rail and Road (ORR) said its inspectors were content that driver-only operations are safe.
Ian Prosser, ORR director of railway safety and HM Chief Inspector of Railways, said: "Trains with doors operated by drivers (known in the industry as 'driver only operation') have been in operation in Great Britain for more than 30 years.
"ORR has scrutinised this approach and our inspectors are satisfied that with suitable equipment, proper procedures and competent staff in place, it is a safe method of working."
The Scottish Government urged commuters to consider car-sharing or working from home as an increase in traffic is predicted.
The government discussed contingency plans for the strike at its resilience committee while its chairman urged both parties to resume talks urgently.
A multi-agency response team - involving Network Rail, ScotRail, Traffic Scotland, Police Scotland, and rail operating companies - will be set up to monitor events on Tuesday.
Committee chairman Humza Yousaf said: "It's very disappointing to see industrial action set to go ahead on our railways and we continue to urge further dialogue between ScotRail and the RMT union.
"The walkout will have a significant impact on rail passengers who depend on these services, so I urge both parties to get back round the table immediately and work towards an agreement so that strikes can be avoided.
"If scheduled strikes go ahead, passengers should prepare for significant disruption on the railways on Tuesday.
"ScotRail have published information on how services will be affected, but we would also ask commuters to think now about the changes that they could make to help ease the pressure on the rail network.
"This could include working from home, car-sharing, avoiding travel at peak periods or using buses to get to work."
He added: "Travel operators' websites, Travel Line and Traffic Scotland will have all of the latest information and people should plan ahead and leave more time for their journey.
"Those travelling to the islands by ferry should also consider alternative options in relation to rail connections.
"The Scottish Government's priority will always be to ensure the safety and efficient running of our railways."
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