Delegates and commuters have been told to prepare for transport chaos during the Cop26 summit in Glasgow after ministers admitted they were "not optimistic" that a deal to avoid rail strikes would be agreed before Wednesday's deadline.
Graeme Dey, the SNP transport minister, on Tuesday lashed out at the RMT union, which is planning a 12-day walkout from Monday which would cripple Scotrail services during the climate conference.
He claimed union leaders had repeatedly "moved the goalposts" in pay talks and said his focus would shift to putting back-up plans in place if a compromise was not found by 5pm on Wednesday.
A strike would mean chaos for thousands of Cop26 delegates who have booked accommodation outside Glasgow on the basis that they could easily reach the city by train, as well as people who rely on the rail services to get to work.
On Tuesday, the UN was still advising delegates to take the train to the conference because it is "the most sustainable way" to travel – suggesting many may be surprised to find services not running if the strikes go ahead.
The RMT's industrial action is part of a number of strikes set to take place during the conference, with Glasgow refuse workers also planning to down tools for a week.
The Scottish Liberal Democrats said they would push for Mr Dey to quit if he failed to get trains running, while the Scottish Tories joined calls for the RMT to back down, claiming strikes could prevent NHS workers getting to hospital and would damage Glasgow's reputation around the world.
Jill Reilly, the Lib Dem transport spokesman, said: "The travelling public have now had six months of reduced services on the railways – it's not like this has come out of the blue. If the trains don't run smoothly and on time for the duration of Cop26, then Graeme Dey should resign."
Mr Dey told the BBC: "This is a situation that we have tried extremely hard to avoid. We find ourselves in a perplexing and deeply disappointing situation.
"The RMT keeps moving the goalposts. If there are strikes during Cop26 then we have to prepare for that, not just to move delegates but also for the wider travelling public who will be disrupted by this. We have contingency plans ready, and we have to pivot towards implementing those plans in detail."
The deal on offer includes a 4.7 per cent pay increase over this and next year and a £300 payment for Cop26. Other transport unions have accepted it, but the RMT has described it as "pitiful" and claimed it came with conditions that could cost jobs.
Mick Hogg, the RMT's Scotland organiser, insisted the union wanted to reach an agreement and described Mr Dey's comments as "nonsense".
"The goalposts were never there to be moved in the first place – we have been stonewalled for the last 18 months," he said. "All of a sudden because of Cop26 there's a rush to get around the table in order to find a resolution to the current disputes."
Up to 30,000 people will descend on Scotland's largest city over a two-week period from this week. It was suggested this week that delegates will be advised to travel to the conference by road if trains are not running.