Bus Éireann is to implement cost-cutting measures on 13 January after it said unions rejected a hearing at the Labour Court.
Overtime, shift, premium and rota payments are to be reduced and annual leave will be cut.
There will be a longer working week for clerical and executive employees.
Bus Éireann says the measures are required as the company is facing annual losses of €16m if no agreement is made.
Overtime rates will be reduced from 1.5 times to 1.25 times and there will be an increase in the working week for clerical and executive staff from 36 hours to 39 hours.
There will be a reduction in shift, premium and rota payments, to be reviewed in 2014.
Annual leave will be reduced by three days for the next three years.
A range of allowance and expense payments will also be reduced by 33.3%.
The National Bus and Rail Union has said Bus Éireann's plan has come as a "huge surprise".
The union, which represents 1,200 workers or around 50% of the workforce, said it had been in lengthy discussions with management about 16 issues in a cost recovery plan.
It said the company referred half of those issues to the Labour Relations Commission, where the sides did not make much progress.
After that the union says the company wanted to refer all of the issues to the Labour Court.
The union says it was not in a position to go to the Labour Court because all of the issues had not been discussed at local level.
NBRU Secretary General Michael Faherty said he was expecting a call for further discussions at the LRC. Then, he said, this plan for changes to terms and conditions, to come into effect from next month, arrived on his desk this morning.
The NBRU says it will now have to ballot its members to see if they want the union to prevent the company from implementing the plan without agreement.