Rail unions are considering four more days of strike action in Scotland, BBC Scotland understands.
First Minister Jack McConnell has urged the RMT rail union to call off its "unnecessary and unacceptable" strike and return to the negotiating table.
Network Rail said it believed the RMT was planning four days of strike action next week in the dispute over proposed changes to signal workers' shifts.
However, the union denied any decision about further action had been taken.
The RMT's executive committee is due to meet in Glasgow on Friday to discuss the dispute.
Rail passengers have experienced two days of disruption after workers walked out at 1200 GMT on Wednesday.
Many services have been cancelled and others will operate on a reduced timetable until Friday lunchtime, when the strike ends.
The issue was raised at Question Time in the Scottish Parliament, where the SNP's Nicola Sturgeon accused the Scottish Executive of doing too little.
She said the first minister should have been "knocking heads together" to ensure that the strike did not take place.
Around the table
Mr McConnell said: "The reality here is that passengers on our railways should come first.
"I regard the strike yesterday, today and tomorrow as unnecessary and unacceptable."
He said Network Rail had told him that they would meet the union "within an hour" if the strike was called off and the union was willing to sit around the table with the company.
"I believe that is an offer the trade union should accept," he said.
Mr Crow defended the decision not to go to Acas
"Even if the trade union had a point, they have made their point in the first 24 hours of this dispute.
"They should immediately call off the second 24 hours, get round the table with Network Rail this afternoon, and solve this dispute in the interests of passengers across Scotland."
STUC general secretary Grahame Smith said his comments were "ill-advised and ill-judged".
The RMT has warned that the strike could spread to the rest of the UK.
RMT general secretary Bob Crow said the union had not gone to the arbitration service Acas as "they are not binding by law" and because an agreement was already in place.
How the rail strike has hit some travellers
Transport Minister Tavish Scott told the BBC's Good Morning Scotland programme that Mr Crow's comments were a "throwback to the 1970s".
The first rail strike in Scotland for nearly four years came after talks collapsed on Monday.
Nationally, the union and Network Rail agreed last July to introduce a 35-hour week.
The dispute centres on how that change will be implemented.
Train operator First ScotRail urged passengers to check its website to find out which services were operating.
No trains were running north of Stirling, and those operating further south were operating on a reduced timetable.
The Glasgow to Edinburgh service ran every 15 minutes every first hour and then every 30 minutes for the rest of the day.
Extra buses have been put on standby in various parts of the country to cope with increased demand.
HOW PASSENGERS HAVE BEEN AFFECTED ACROSS SCOTLAND