Four more strikes by ScotRail conductors were announced today by the RMT union.
The latest dates bring the total to 15.
Walkouts will be staged on Sunday 7, Monday 8 Thursday 11 and Saturday 13 August.
These come on top of the previously-announced strike this Sunday.
The news confirms the union telling The Scotsman yesterday that it was poised to organise more industrial action.
The stoppages are likely to hit one in five trains, with no services on some lines and replacement buses on others.
Where conductor-operated trains run - everywhere outside Strathclyde - frequencies will be cut and services limited to around 7am-7pm.
The dispute is over ScotRail plans to downgrade conductors, or guards, on a new fleet of trains due to be introduced across the Central Belt from next year.
Control of doors and overall passenger safety would be switched to drivers, with ticket checks on some routes transferred to lower-paid ticket examiners.
The RMT said it had no option but stage more strikes.
A spokesman said: “The RMT has repeatedly attempted to engage in serious talks through [conciliation service] Acas, but progress has been blocked as the company have tried to pick and choose issues and divide and rule the workforce.”
RMT general secretary Mick Cash said: “The workforce knows only too well there is a very real threat to passengers of watering down and wiping out the safety-critical role of the guard on these ScotRail services.
“That is a lethal gamble with basic rail safety.
“We have had fantastic support from the travelling public for our action as passengers know full well that this strike is all about their safety.
“The union remains available for serious and meaningful talks.”
A ScotRail spokesman said: “Sadly, this type of behaviour from the RMT has been all too common during this dispute.
“They say that they are open to talks, but their words are not matched by their deeds.
“Just this afternoon, we held discussions with the RMT which we would describe as encouraging.
“We talked through some ideas and we agreed to come together again to discuss them further.
“It really is the most extraordinary act of bad faith for the RMT to leave these positive talks and to immediately announce another round of strikes.
“These needless strikes are really hurting our people financially.
“We have guaranteed the jobs, pay and terms and conditions for our conductors, and we have said we will always schedule a second member of staff on board to look after our customers.”