Fresh talks are being held between ScotRail and train drivers' union Aslef in a bid to resolve an industrial dispute which has hit Sunday services.
Train drivers' union Aslef and the owners of ScotRail have said good progress has been made in talks over pay and conditions.
The move came as Aslef announced it would ballot its members for industrial action which could see Sunday services grind to a halt next month.
The talks were called in a bid to resolve an industrial dispute which has hit Sunday services.
ScotRail has offered drivers a 2.5% pay rise and a one-off bonus.
They follow moves by Aslef to ballot its members for industrial action from next month.
But talks stalled after the union accused the operator of trying to push through new terms and conditions.
The dispute centres around plans by ScotRail franchise holders Abellio to introduce a seven-day rota for drivers.
The franchise was taken over earlier this year by Dutch firm Abellio, which said it had inherited a seven-day railway that only had a six-day rota system for drivers, with Sunday services dependent on volunteers.
Currently drivers work a six-day week, with Sundays classed as overtime.
The union has said it does not object to the plans, but wants to see drivers given a pay rise for the extra work.
About a third of ScotRail's trains were cancelled on Sunday after drivers refused to work overtime.
About a third of ScotRail's trains were cancelled on Sunday after drivers refused to work overtime.
Kevin Lindsay from the train drivers' union ASLEF says they were left with no choice but to ballot members for industrial action after negotiations with Abellio broke down.
Aslef has warned that industrial action could start as early as 17 August, if no settlement can be reached and members back action.
He said a 2.5% pay offer was based on productivity, which the union would not accept.
The talks are due to continue on Wednesday.
"It is 2.5% overall, but 1.4% of that is funded by train drivers having shorter breaks, changes to their availability and flexibility, and a reduction in training. These things are just unacceptable to train drivers," he told Good Morning Scotland.
"We take the action with a heavy heart, but it appears to have had some kind of effect, because Abellio are meeting us this morning," he added.
Mr Lindsay said that industrial action could start as early as 17 August, if no settlement can be reached.
