SIPTU has said strike action will go ahead as planned if there is no positive outcome from talks with Bus Éireann management over planned cutbacks.
Union representatives and Bus Éireann management have accepted an invitation to engage with the Labour Relations Commission today.
Bus Eireann announced in early December its intention to unilaterly implement change to staff terms and conditions after trade unions rejected a €9m cost-saving plan.
The company wants to reduce overtime rates, increase the working week for some staff, reduce shift, premium and rota payments, and cut annual leave by three days, with effect from this Sunday.
Members of the National Bus and Rail Union say their action will commence on Sunday, while SIPTU and the TSSA plan to mount pickets next Thursday.
SIPTU's Willie Noone said he could not understand why management had decided to leave the unions out of the process.
"Our members know that cuts are probably going to come, but they're not going to allow the company to pick and choose just what cuts are coming," he said.
"We have to have an input into whatever cuts are coming, and whatever change in work practices come about."