Bank branches in Dublin and elsewhere on the east coast could begin running out of cash by the weekend unless a row at the security firm, Brinks Allied, is settled.
Employees of the company yesterday rejected proposals aimed at resolving the dispute, over an attempt by management to introduce new vehicles and security procedures.
Staff claim the new methods would leave them more vulnerable to attack by armed robbers and have refused to implement them. Cash deliveries are currently not being carried out because, although staff have been reporting for work, the company insists they must apply the new procedures.
To date, only non-branch ATM machines have been affected. By yesterday, 160 of these - 80 per cent of the total - were out of service as a result of the row.
Over the next 24 hours, however, about 80 ATM machines at bank branches are also expected to close.
SIPTU, and the company yesterday agreed to refer the row to the Labour Court, which is expected to convene a hearing today or tomorrow.
If there is no immediate resolution, the Irish Payment Services Organisation, which represents the banking industry, has warned that the effects of the dispute could immediately worsen.
There are also fears that the row could jeopardise the jobs of up to 200 people employed by Brinks Allied in Ireland.
A spokeswoman for the IPSO, Ms Una Dillon, said cash supplies to branches could begin to be seriously disrupted by the weekend.
"If there is no resolution then it will become an issue for branches within days. This could involve branches running out of cash."
AIB, Bank of Ireland and Ulster Bank are clients of Brinks Allied, so their branches in the east would be affected.
Bank branches in other parts of the State are not involved because they are serviced by other security firms.
Ms Dillon said the IPSO was "very disappointed" that settlement proposals drawn up at the Labour Relations Commission on Tuesday, and recommended by both SIPTU and Brinks Allied management, had been rejected by staff. The 60 workers directly involved voted by 42 to 18 not to accept the proposals.
Mr Kevin McMahon, SIPTU's security branch secretary, said the proposals had successfully addressed one of the most contentious issues, the instruction to van drivers to drive away from a threatened colleague in the event of a robbery.
However, there were other elements which had not gone far enough to address employees' concerns.
Details of the proposals were withheld, at the company's request, for security reasons.
Mr McMahon said he was concerned the row could jeopardise Brinks Allied's Irish operation.