Bus Éireann is expected to outline tomorrow whether it will press ahead with unilateral cuts to employee pay.
Customers are facing no services with the prospect of an all-out strike following the collapse of talks at the workplace relations commission yesterday.
Management, along with the board of the company, have been meeting today to discuss the situation.
Tonight, the NBRU have written to the National Transport Authority and the Department of Transport asking them to get involved in the crisis.
They say that they are seeking "positive intervention at this crucial juncture before and all out dispute causes havoc".