NBRU say a strike is on the cards, unless management change their approach
Unions and management at Bus Éireann return to talks at the Workplace Relations Commission (WRC) on Tuesday.
Management has outlined €30m in savings, which it says are vital to save the company.
But the NBRU and SIPTU say they will not accept the reduced pay and conditions being proposed.
The NBRU say a strike is on the cards, unless management change their approach.
It follows the release of a document to staff about cost-cutting measures prior to its full discussion at the meeting.
SIPTU have officially complained to the WRC about the document and believe it may have been released maliciously.
SIPTU sector organiser, Willie Noone, said: "The talks are now at a critical stage but we believe that the company has come around to our position, that its workers and the public will not accept a low wage, low service model for public transport.
"The company must be honourable and respect the State’s industrial relations institutions and this means implementing an outstanding Labour Court recommendation on drivers pay in full.
"If this is done progress can be made in these talks but only on the basis that our members do not have to endure a deterioration in their pay, or terms and conditions of employment."
The document outlines ways to cut costs to wages, potential route closures and redundancies.
Martin Wall is industry correspondent with the Irish Times.
He told Newstalk Breakfast: "For the public, I think the big issue would be the routes - the company says it wants to cease operating three routes: that's Dublin - Derry, Athlone to Westport and Dublin to Clonmel.
"Although the Government has insisted that connectivity to rural towns would be continued, we don't know the nature of those arrangements.
"It reinstated the proposals in relation to cuts to the earnings - to overtime rates, premium payments - there would be major work practice changes".
The document also says that average earnings for bus drivers are around €32,000 a year, but this can go as high as €47,000 with premium payments.