Ministers called for the strike to be suspended and the latest pay offer to be put to a members' ballot.
The five-month-old dispute involves more than 2,000 RMT members including train conductors and station staff.
The union has been offered a 5 per cent increase but is seeking 8.2 per cent.
It has already staged a 24-hour strike on Monday which halted all but three routes in the biggest disruption to ScotRail this year, far more than during the series of walkouts by signallers at UK Government-owned Network Rail in a separate pay and conditions dispute.
ScotRail said the overtime ban had led to four cancellations on Friday because of a shortage of conductors.
Two were on the main Edinburgh-Glasgow route via Falkirk High and two on the Alloa line.
The RMT said the impact would be far greater on Sunday because it is not classed as part of the working week.
Passengers are warned to check before travelling.
ScotRail head of customer operations Phil Campbell said: "We are assessing the impact the strike will have on our services and working on contingency arrangements.”
The latest talks between the two sides broke down on Thursday, but both said they were available for further meetings.
A ScotRail spokesperson said: “We met with RMT representatives again to hear their views following Monday’s strike action.
“We urged them to give members a say on our very strong offer - a 5 per cent basic pay increase, a six-year job guarantee, a £500 one-off payment for using technology like mobile phones, and much more.”
RMT Scottish organiser Mick Hogg said: “We are disappointed that ScotRail does not have the power or the authority to make an improved offer.
"This is despite offers above 5 per cent being made to refuse workers, teachers and now nurses.”
A Scottish Government spokesperson said: “We absolutely respect the democratic right of union members to take industrial action, and there have been constructive discussions between ScotRail and the Scottish representatives of the RMT members – unlike negotiations elsewhere in the UK.
"So it is really disappointing that Scottish members are being denied the opportunity to vote on a new Scottish deal.
“We call on the RMT national executive to suspend the ScotRail strike action in favour of a members’ referendum on the revised pay offer – an offer which is self-funded, fair and affordable.”
Scottish Conservatives transport spokesperson said Graham Simpson agreed.
He said: “Rail users are fed up with these militant antics from the RMT.
“Union bosses need to call off the strike, put this offer to their members and let them decide.”
“Since nationalisation, relations between the unions and ScotRail have got progressively worse, and the SNP government have been content to sit on their hands oblivious to the misery this is causing passengers.
“This frustrating behaviour across the board has worn thin the patience of Scots who are desperate for reliable train travel.”
Robert Samson, senior stakeholder manager at passenger watchdog Transport Focus, said: “Timely and accurate information must be provided to allow passengers to make an informed decision about their journey options.”