Caledonian Sleeper staff are due to be balloted for strike action over stress caused by their extra workload on its new trains, The Scotsman has learned.
The Rail, Maritime and Transport union (RMT) has told operator Serco it is in dispute and officials are waiting approval for the vote from union leaders.
Confirmation of the ballot would come as a further setback for the firm, which today admitted the introduction of its £150 million new fleet has been further delayed on three routes to the north of Scotland.
READ MORE: New luxury Caledonian Sleeper trains suffer further delay
RMT regional organiser Gordon Martin said: "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."
Mr Martin said managers were trying to introduce new working practices on the new trains which were causing stress and affecting the mental health of staff.
These included having to serve a greater number of passengers.
Mr Martin said he had recommended a ballot for strike action or industrial action short of a strike.
Any ballot is likely to take several weeks to complete, after which the union would have to give one week's notice of any action.
The new trains were introduced on the Edinburgh and Glasgow routes to London last month.
They were due to start operating to Aberdeen, Fort William and Inverness next month but this has now been postponed to July.
The trains give passengers the ability to order food - in addition to breakfast - from their rooms for the first time via an intercom.
Orders have to be delivered from the galley in the Club Car up to six carriages away.
READ MORE: Five staff quit after Caledonian Sleeper train boozing rap
Caledonian Sleeper said it had yet to receive formal notification from RMT so it was unable to comment.