Staff could take strike action over the extra workload of the new Caledonian Sleeper trains, with staff expected to be balloted for strike action over stress caused by their extra workload.

READ MORE: New Caledonian Sleeper trains carry first passengers 

According to the Scotsman, The Rail, Maritime and Transport union (RMT) has told operator Serco they are waiting for approval to ballot staff from union leaders.

HeraldScotland:   

It comes following a further delay to the rollout of the service on Highland routes, with the £130m fleet not expected to operate on northbound lines until early July. 

RMT regional organiser Gordon Martin told The Scotsman: "We had a meeting with the company on Friday when we informed them verbally we were in dispute.

"The introduction of the new rolling stock has caused a lot of stress among the workforce."

READ MORE: First pictures: Caledonian Sleeper trains reveal first look inside new rail fleet 

According to Mr Martin, new working practices on the trains are allegedly causing stress and impacting the mental health of staff. 

A ballot for strike action or industrial action short of a strike is expected to take place with results, if it goes ahead, expected in the next few weeks. 

The new trains, which were introduced on the Edinburgh and Glasgow routes to London last month, were expected to operate to Aberdeen, Fort William and Inverness next month but this has now been postponed to July 7. 

The date is more than a month later than previously announced.