Staff employed by the train drivers' union have voted overwhelmingly to walk out, claiming they have been bullied by their new leader.
Employees of the rail union Aslef - who are members of the GMB general union - have decided by 20 votes to five to take industrial action, alleging that the general secretary, Shaun Brady, has harassed them and tried to switch staff between departments in defiance of agreements.
After the intervention of the TUC leader, Brendan Barber, the GMB has agreed to suspend any strike pending negotiations in a fortnight's time.
As part of the deal Mr Brady has agreed to withdraw an extraordinary letter in which he threatened to sack his entire staff if they went on strike. The letter also warned that he would withdraw recognition from their union. Aslef has been responsible for a series of high profile strikes on the rail network, which have inconvenienced tens of thousands of passengers.
Paul Kenny, leader of the GMB general union in London, said the letter from the Aslef general secretary was meant to intimidate his members into voting against industrial action.
"People were very upset and angry. They are not sure what they could do, short of going on strike, to show how they felt about it. People are not prepared to be intimidated. This is a serious situation."
Mr Kenny warned that if the meeting with Mr Brady on 26 January failed to address his members' grievances "industrial action will follow".
The new Aslef leader, who took over from Mick Rix, has warned employees that he would create a non-union staff association if they walked out, cut their wages and withdraw a wide range of fringe benefits.
Mr Brady believes the dispute has been manufactured by supporters of his predecessor who are trying to undermine his leadership. He also alleges that he has been forced to sort out "financial irregularities" left by the previous regime.