ScotRail fares have increased by an average of 3.2 per cent , with peak tickets going up by 3.6 per cent .
The union said the rise - the biggest in five years - comes at a time when earnings are falling in real terms.
Its members will be leafleting passengers at several stations on Wednesday to highlight the case for public ownership.
RMT general secretary Mick Cash said that while revenues for ScotRail operator Abellio would increase, rail travel is “becoming increasingly unaffordable for many”.
He added it was necessary to “bring a permanent end to the damaging fragmentation and privatisation of our railways”.
Scottish Labour also contrasted the fare increases with a fall in earnings.
Figures from the Scottish Parliament Information Centre show salaries fell by 1.6 per cent last year when inflation is taken into account.
Real-terms pay has increased by 1.8 per cent since January 2013, however regulated fares have increased 12.7 per cent over the same period.
Labour MSP Colin Smyth said: “The SNP seem to think passengers in Scotland are getting a fair deal. They’re not.
“Passengers in this country already pay some of the highest fares in western Europe and now ticket prices are going up again.
“Rail fares have increased faster than wages over the last five years and that is unacceptable, particularly given the ongoing delays, cancellations and overcrowding rail users experience with ScotRail.”
“Scottish Labour would take ScotRail back into public ownership and deliver a people’s railway that puts passengers first.”
A Transport Scotland spokeswoman said: “Scotland’s rail fares increase is lower than inflation and lower than the average increase across the UK.
“We are currently undertaking a review of the National Transport Strategy, which will consider our long-term approach to ensuring the affordability of transport across Scotland.
“We want to see more people take the train and we recognise that this means prices have to be affordable and fair.
“Steps are being taken to ensure that a public sector operator is able to bid for a future rail contract, and that there is a public sector body able to do so.
“We secured the right for a public sector operator to bid for the franchise, despite repeatedly being denied by successive Labour and Conservative governments.”