Strike action is planned to coincide with the climate summit which will see thousands of delegates from across the globe, including world leaders such as Joe Biden, arrive in Scotland for crucial climate change talks.
The summit is to get under way on October 31.
RMT General Secretary Mick Lynch said: "There was a golden opportunity for ScotRail to make serious progress in talks today but instead they offered nothing of any consequence and as a result our action throughout COP26 goes ahead as planned.
"There can be no climate justice without pay justice and it's about time ScotRail, the SNP and Transport Scotland woke up to that fact. The same message applies to our Scottish Caledonian Sleeper members.
"There is still time to avoid the chaos of a transport shutdown during COP26 if the key players get back with some serious proposals. We remain available for talks but the ball is firmly in their court."
ScotRail management and RMT representatives met to discuss what could enable an agreement to be reached to settle the ongoing dispute after an offer was made two weeks ago.
Ian McConnell, ScotRail Chief Operating Officer, said: “I’m disappointed and incredibly frustrated that RMT representatives have point blank rejected our latest proposal.
“The RMT leadership, despite stating that the only matter needing to be resolved was rest day working, have now moved the goalposts without consulting their members. It can only indicate they’re not serious about moving forward and delivering a successful COP26.
“Time is now running out to reach agreement and, despite a pay offer of 4.7 per cent over two years, a £300 payment for COP26, and a rest day working enhancement, it seems RMT bosses are intent on sabotaging Scotland’s Railway’s role during COP26.
“With the threat of industrial action remaining, we’re continuing to develop contingency plans to provide a core service for the duration of the summit.”