Secretary general of the NBRU Michael Faherty said that his union has a mandate from members to take industrial action if the company presses ahead with cost-cutting measures.
Bus Eireann is standing firm against the threats and said that the €5m reductions are necessary.
However, Mr Faherty said that members of the union could not afford to take the loss in take-home pay.
The NBRU represents 1,100 of the company's 2,500 staff – a final ballot on strike action is taking place today.
Fianna Fail's transport spokesman Timmy Dooley said that while it was clear that Bus Eireann needs to make savings, these "weigh far too heavily on the workers" who earn an average of €33,000 a year.
"The workers are being asked on average to take a hit of €3,000," he told the Herald.
"That is a phenomenal amount on workers' pay."
He said that State subvention for Bus Eireann is the lowest of any major national public bus company in Europe and said that the Government needs to step up its support for the group.
Mr Dooley said that any strike action will have a major impact on the transport system.
"Strike action will cause considerable inconvenience to the travelling public – work, school and college," he said. "There are 114,000 students who will be affected if the dispute spreads to the school transport network."
Bus Eireann representative Andrew McLindon said that the process has reached the end of the road.
"Since June 2012 there have been months of internal talks, two days of hearings with the Labour Court and talks with the Labour Relations Commission," he said.
"Everyone is agreed that the company is in a very different financial situation and it needs the savings from payroll in order to protect the viability of the company, in order to protect the 2,500 jobs."
And he said that the company fully intends to press ahead with the planned cuts.
"We certainly will. We have a LC recommendation our intention is to implement the LC recommendation," Mr McLindon said on Morning Ireland.