It came as today’s 5pm deadline neared for the latest ScotRail pay offer of 4.7 per cent over two years to be accepted before it was taken off the table.
However, the operator has not said whether it is considering a reported new demand made by the RMT on BBC Scotland yesterday for a one-year, 4.9 per cent increase.
Mr Dey did not respond directly to MSPs who asked him whether the demand had been accepted or rejected.
The RMT has called strikes from Monday until Friday 15 November, which could have a significant effect on the thousands of people expected to travel to the COP26 climate change conference in Glasgow being held over those two weeks.
Mr Dey said “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 told him: “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.
"We are not going to indulge in digging deeper trenches when there is ample time to resolve these disputes if we get talks back on.
"We are ready and waiting to get back round the table and Mr Dey should be focusing his efforts on making that happen."
ScotRail has set the 5pm deadline so it can put contingency measures in place should the strikes go ahead.
However, only some trains on the Edinburgh-Glasgow line via Bathgate, and a shuttle Glasgow Central and Exhibition Centre, beside the COP26 venue, are likely to run.