SIPTU has told its members at Bus Éireann to get ready for a "hard battle and struggle" during an all-out strike as the company prepares to set a date for €12m pay cuts.
In a 'strike notice update' it warned industrial action is unlikely to end "in the short term".
Unions are set to mount pickets if the company rolls out the cuts without agreement, following the breakdown of talks at the Workplace Relations Commission during the week.
It is understood that the company has red-circled 120 jobs to go - 60 managerial, executive and clerical roles, 40 engineering and maintenance positions, and 20 inspectors - although it is unclear how many drivers will be affected.
Acting chief executive Ray Hernan is finalising the cuts as the company faces the threat of insolvency in May.
Preparations are gathering pace for a strike, as banners and placards will be distributed to garages around the country from head office in Liberty Hall this weekend.
The Siptu information notice said that Bus Éireann management and its "expensive" consultants' decision to end talks made it "glaringly obvious" that plans will be pushed ahead to exit Expressway.
It said the company's financial difficulties were being used to eliminate conditions of employment, with the only exception given to managers at the highest level with enhanced voluntary severance packages.
"As it is becoming clear to Siptu that an indefinite strike is now becoming unavoidable due to the inertia and inaction shown by the Department of Transport, the National Transport Authority, the Transport Minister and the fact that TDs in Government from rural areas in particular are gone into hiding, the focus now must be to prepare for the hard battle and struggle that lies ahead," it said.
It said due to the "savage" pay cuts since 2009, "this dispute has all the ingredients of guaranteeing that the dispute will not be a dispute ending in the short term and hence we must prepare accordingly."
When industrial action begins, it said all Siptu members are expected to participate in the strike.
"All categories have given a very strong mandate for this action in a ballot and hence all categories are asked to work together in organising the picketing duties and the necessary administration of the dispute," it said.
It said that school bus drivers are not involved yet - but this is being "constantly reviewed".
It claimed Bus Éireann workers are the first to be targeted by CIÉ to drive down wages and such attacks "must be thwarted".
"The Siptu members in Bus Éireann can have the assurance that this union is prepared and will not be found wanting in defending the jobs that you and your families depend on," the notice from Transport Sector Organiser Willie Noone said.
"In circumstances where rural TDs would give the same assurance regarding defending services in their areas, this dispute could be avoided and members are asked to remind their local representatives of this fact and the fact that an election is not too far away."
Sources revealed that Dublin Bus drivers based in Broadstone have been asked to move buses to the Harristown garage.
Their entrance is beside the Bus Éireann one and the move is seen as an attempt by management to avoid difficulties getting tour buses past pickets if industrial action goes ahead.
The Nbru has written to the secretary general of the Department of Transport, Graham Doyle, to hold a forum involving the department and National Transport Authority to find a resolution.
Sources have revealed that 120 managerial, maintenance and inspector jobs have been earmarked to go. The number of drivers to be targeted is unclear. Some sources claim up to 516 workers may go across the company.
It is understood that a new role will be created to replace inspectors, with a salary of €50,000 a year.
*Sources said a panel of casual drivers will be set up on a banded hour arrangement of a minimum 20 hours a week.
*Allowances and expenses to be cut by 10pc.
*The axing of shift and rota allowances.
*A Sunday premium payment will be reduced to 20pc of its current value.
*Overtime rates will be reduced for public holidays.
*All wage increments will cease from March 31 this year.
*No overtime for training or staff attending meetings.
*Unplanned bus hire will not be sanctioned.
*Flexitime for clerical staff will stop.
*There will be no cash payments to staff. Around 1.5pc of staff are paid in cash.