About 35 employees of the train drivers' union Aslef, mainly based in London, will vote in the New Year.

It follows claims of bullying and harassment which have been denied by Aslef's general secretary Shaun Brady.

Staff, who will be represented by the GMB union, are also said to be worried about job losses because of re-organisation proposals.

Some employees are said to be off sick with stress.

Mr Brady, who took over as general secretary from Mick Rix earlier this year, said the claims were "absolute rubbish".

He said he was prepared to meet the GMB to resolve the dispute.