Dublin Bus has said it will not be able to provide a service from this Sunday if planned industrial action goes ahead.
SIPTU and the National Bus and Rail Union (NBRU) served strike notice on the company earlier this week, after Dublin Bus told them it would implement productivity and cost reduction measures from Sunday.
Speaking on RTÉ's Morning Ireland, Dublin Bus spokeswoman Clíodhna Ní Fhátharta said that the size of the Dublin Bus operation meant it was not possible to put a contingency plan in place.
"The best contingency plan at the moment is that people would come into work, and we would urge them to reconsider that and not disrupt our customers."
According to Dublin Bus, it needs to save €11.7m to return the company to financial stability.
Dublin Bus said it has spent 14 months negotiating productivity and cost reduction plans with unions. In June, the Labour Court backed the company’s plans.
However, when balloted, SIPTU and NBRU members rejected them and threatened strike action.
On Monday Dublin Bus said the measures would come into effect this Sunday.
Both unions subsequently served strike notice on the company.
Minister for Transport Leo Varadkar said public transport should be run in the interests of the passengers who use and not in the interests of management or unions.
Minister Varadkar said: "There is no more room for delay. Both sides should do everything to agree the necessary savings in order to avoid disruption on Sunday."
Customers facing disruption from Sunday
SIPTU's transport organiser Willie Noone said staff at Dublin Bus are not willing to return to work after Sunday's strike action if the company insists on implementing its current cost-reduction plans.
Speaking on RTÉ's News at One, Mr Noone said the union would welcome further discussions as an alternative to strike action.
"If the company come along, even at the last moment, and say 'we're not going to implement the cost-cutting', yes, the strike will be over.
"But if they say to us they are going to continue on Monday and Tuesday and Wednesday, well our members are not willing to go back on those terms," he said.
The company said it will be informing customers in the coming days about potential disruption.
The Department of Transport said savings need to be found and there have been extensive discussions to that end.
The department said it would like to see further engagement in order to avoid disruption to services and passengers.