The train operator and Aslef are at loggerheads over pay rises for drivers, with the company's latest 6.4% offer being rejected.
However, further conflict has arisen after several train services in and around Glasgow Central were cancelled on Sunday afternoon due to understaffing.
ScotRail blamed Sunday's rail disruption in the west of Scotland on "drivers not covering shifts", a claim disputed by Aslef's general secretary Mick Whelan.
Mr Whelan accused the train operator of placing the blame on drivers in an attempt to preclude any potential industrial action.
He said: "The company is attempting to use our current 2013 pay dispute to implicate our members for their failure to provide a service without disruption.
"It is Aslef's view that this was an irresponsible and inflammatory move on the part of ScotRail which misled members of the public and potentially exposed train drivers to abuse and harassment.
"We will not be dissuaded by these unscrupulous tactics from affording our members the democratic right to vote on, and take part in, industrial action should that be the decision of the majority."
ScotRail and Aslef have been in discussions for the past few months in an effort to end the drivers' pay dispute. However, stalemate in negotiations has prompted the drivers' union to hold a ballot for industrial action.
If the union members return a "yes" vote then all train services on Sundays in Scotland will be suspended.
ScotRail has expressed its dismay for the degraded timetable although it has scheduled negotiations with Aslef for later this week.
Union members have already declined two offers from the train company, including the 6.4% increase which would have taken their basic annual pay to just under £42,000.
Representatives of Aslef insist their members remain undervalued, and say they are among the poorest-paid train drivers in the UK.
Sunday shift patterns have also proved contentious, with train services suffering as a result.
ScotRail is adamant that drivers are contracted to work at least one Sunday every three weeks and any additional Sunday work is voluntary. A full Sunday timetable is therefore reliant on many drivers working overtime.
Kevin Lindsay, district organiser for Aslef Scotland, has warned that unless agreement can be reached over pay, the cancellations suffered by travellers on Sunday could be widened across the west of Scotland in the coming weeks.
He said: "It's simple really. ScotRail do not have enough drivers to cover the seven-day service they're contracted to provide.
"Drivers are obliged only to work six days a week and the Sunday services have been long been reliant solely on overtime.
"The suggestion that last Sunday's service disruption was due to drivers simply 'not turning up for their shifts' is scurrilous.
"ScotRail are not telling the public the whole story and Sunday's disruption was not the result of any organised action on our part."
He added: "For now we are currently in discussions with ScotRail in hopes of avoiding any kind of formal industrial action.
"However, a yes vote to ban overtime will mean no Sunday services at all for the whole of Scotland."
The result of Aslef's ballot is due on October 18.