The trade union has asked the 8,000 bank staff for mobile phone numbers and private email addresses to enable it communicate with them at short notice.

In a memo, it told them: "As you are well aware we are facing one of the biggest challenges ever in our union's history and, for us to meet that challenge and ensure that our members' jobs, terms and conditions are protected into the future, it is imperative that we are in a position to issue instant guidelines and directives to every member."

Because of the heated nature of the dispute, which arises from the bank's decision to shut its main pension scheme to new staff recruited after 1 October, the Labour Court is not expected to give its adjudication until after Christmas.

The IBOA is already planning its response should the bank decide not to comply with a Labour Court decision that went in the union's favour.

This is likely to include the threat of strike action.