It came as the union said it had received a new offer from ScotRail but did not provide details.
The Rail, Maritime and Transport union (RMT) is now seeking the same 2.5 per cent increase for this year as it was offered, but without strings – various productivity improvements.
Its proposal also includes the £300 COP26 payment and increase in rest day working payments that were previously offered by ScotRail.
However, the union does not want to take up a 2.2 per cent offer for next year as part of the original ScotRail package.
The train operator had given the union until 5pm today to accept its offer or it would be withdrawn.
RMT general secretary Mick Lynch said: "We are making this offer in good faith with the sole intention of breaking the current deadlock and allowing us to make progress as the clock ticks down to COP26.
"We await a positive response from the company.”
In a letter to ScotRail, he wrote: “The following is RMT’s final position, which I understand is different from what you required, but nevertheless is my union’s final position on pay and hope you can give this proposal due consideration.”
It comprised a one-year 2.5 per cent pay increase from April 2021, an extra three hours’ pay for rest day working and the £300 COP payment.
The union would negotiate a separate increase from April 2022 at a later date.
A ScotRail spokesperson said: “A proposal has been submitted by the RMT just before the deadline.
"As you would expect, we are giving it due consideration.”
If the threatened 12 days of strikes go ahead from Monday, most ScotRail trains would stop.
However, the operator plans to run some services on the secondary Edinburgh Waverley-Glasgow Queen Street line via Bathgate and Airdrie.
It is not yet know how often trains would run but they are likely to be limited to six coaches compared to eight on the main route between the two cities.
A shuttle service is also planned between Glasgow Central and Exhibition Centre, beside the Scottish Event Campus where COP26 is being held.
However, the lack of other trains would cause significant disruption for regular passengers and the thousands of people expected to travel to COP26.
Meantime, transport minister Graeme Dey accused the RMT of changing its position numerous times which had made it “very difficult to establish trust”.
He told MSPs: “Multiple times over recent weeks we have been led directly and publicly to believe that there was a possible resolution of this dispute.
"This government and ScotRail reached out on all occasions, only to find the goalposts moved.
"It has been very difficult to establish trust in this process.
"On a number of occasions, a proposal has appeared to have been put forward by the RMT and then it has changed.”
But former Scottish Liberal Democrat leader Willie Rennie said: “I’m not sure the minister’s increasingly aggressive language towards the RMT is going to resolve this issue.”
RMT general secretary Mick Lynch said: "This inflammatory language helps no one.”