The RMT rail union has said a gun is being pointed at its head after a Wednesday deadline was set for accepting a pay offer that would avoid a strike during COP26.
Members of the union who work for ScotRail will strike during the two-week global climate conference in protest at pay and conditions, with action due to begin on November 1.
Its workers on the Caledonian Sleeper are also set to strike.
The Scottish Government said it will focus on “making alternative plans for rail operations during COP26” if ScotRail’s offer is not accepted by Wednesday.
RMT’s AGM in Leeds on Monday voted to reject the latest proposal.
The union’s general secretary Mick Lynch said: “We have been given a wholly arbitrary deadline of 5pm on Wednesday to accept this deal or the whole pay offer will be pulled.
“You cannot conduct serious negotiations with that sort of gun pointed at your head.”
He added: “Our message to Nicola Sturgeon, Transport Scotland, Abellio (operator of ScotRail) and Serco (operator of the Caledonian Sleeper) is that there is still time to resolve the pay disputes but it requires some serious movement, the lifting of bogus deadlines and genuine talks.
“The union is available to get those talks on anytime, any place, anywhere. ”
Rail services in Scotland have been crippled for months by strike action, with few trains running on Sundays.
Three other unions have since settled their disputes with ScotRail.
Scotland’s transport minister Graeme Dey said he was “utterly perplexed at the position the RMT leadership is taking”.
He said the most recent offer to the union, which was made on Sunday, consisted of a 4.7% pay increase over this and next year and a £300 payment for COP26.
It also included an additional payment equivalent to three hours salary for booking on for a rest day shift for the rest of the year, he said.
The minister said the pay offer was “fair and good”, adding: “We understood that we were close to agreement with negotiators apparently happy with the offer, RMT leaders have then moved the goalposts”.
He said: “What the RMT is now asking for is neither reasonable nor affordable.
“The travelling public deserve and need to know what rail service will be operating in the next two weeks.
“That is why we put a deadline of Wednesday for this offer to be accepted – the enhanced offer remains on the table until then.
“At that point, we must focus on making alternative plans for rail operations during COP26.”
He added: “There is still time to avoid a situation which no-one surely wants, where train services are severely disrupted and hardworking RMT members lose out – but following this decision by the RMT, regrettably that is where we may now find ourselves.
“ScotRail will now go ahead and honour the pay offer for those unions which have accepted it and also those who are not members of unions.”