Bus Eireann have told their employees that management will impose cuts to work practices without agreement.
Staff at the loss-making company received a letter that approved the implementation of 46 changes to work practices, without further measures expected early next month.
The review of the company, which will result in job losses, will be presented to the board next Monday.
In a letter to staff, Acting Chief Executive Ray Hernan said: “Maintaining the status quote now is simply not an option”.
Passengers could face travel disruption as it is expected that union members will respond by taking to the picket lines.
Unions have already warned management that implementing cuts without agreement with staff may lead to an all-out strike.
Mr Hernan said unions had indicated a willingness to negotiate and accept a loss of over time earnings - but only in relation to ad hoc overtime.
He said at the current rate of losses, the company would be insolvent within a matter of months; and said there was no basis for talks reconvening so difficult decisions had to be taken.
Dates to axe or reduce services on five separate routes have also been set: route X7 will be withdrawn on April 2, and the X12 and 20/X20 services will be reduced on the same date. The number 21 will go on April 16 and number 833 on June 25.