The NBRU says the company has made a 'declaration of war' on its workers
Bus Éireann says school transport should not be affected by strike action due to get underway tomorrow.
Unions this afternoon confirmed an all-out strike will take place from midnight amid the ongoing dispute between unions and the transport company.
The company has warned it risks insolvency within months if it does not implement a range of cost-saving measures - including changes to workers' terms & conditions.
However, unions have refused to agree to the proposed changes, saying Bus Éireann is "intent on pursuing a race to the bottom in relation to workers jobs".
Workers will now go on strike from 12.01am on Friday.
NBRU General Secretary Dermot O'Leary said it was a "source of considerable regret" that the travelling public will be impacted by the decision, but said there is "extreme and at this stage uncontainable anger" among workers.
He said: "The NBRU will now engage in an all-out indefinite strike from Midnight tonight in response to Bus Éireann’s appalling declaration of war on its own workforce.
"The NBRU remains available at any stage to reengage on an efficiency based agenda in order to resolve the Expressway crisis."
In a statement this evening, Minister for Transport Shane Ross said: "I am deeply concerned at the impact that this strike will have on the travelling public.
"In the last week, both management and trade unions have highlighted their willingness to discuss improvements in the company’s operations and efficiency.
"It is now time for both sides to show this willingness can result in an acceptable and fair agreement that safeguards the company’s future and all of those who rely upon it," he concluded.
SIPTU says the dispute centres around proposed cuts to pay, the casualisation of work and the threat of job losses at the company.
The union's sector organiser Willie Noone explained: “Our members will not accept the destruction of a public service which is essential in connecting communities throughout Ireland.
"Any changes or payroll reductions must be equitable and management, who played a huge role in creating the company’s current financial predicament, must make a substantial contribution," he added.
In a statement, Bus Éireann has said it is 'extremely disappointed' that unions have called a strike.
It says losses for January and February are 41% higher than the same period last year.
"Industrial action will cause major inconvenience to our customers and exacerbate the perilous financial situation at the company," the company said.
"The efficiencies we are seeking to introduce relate to work practices, which must be put in place if the company is to have a viable and sustainable future."
The statement adds: "We apologise to our customers for any inconvenience caused by unions’ action and want to reiterate that School Transport services, GoBe.ie, Eurolines and Cross-Border Translink operated services should not be affected by this strike action."