SIPTU members at Bus Eireann have voted overwhelmingly in favour of strike action at the company.
It comes after members of the National Bus and Rail Union (NBRU) also voted for strike action by over 90% earlier this week.
The NBRU has accused management of trying to impose new conditions of employment from January 13th.
The action is in opposition to CIE plans to change working conditions from this Sunday in a bid to save around €9 million on the company payroll.
SIPTU says the proposed changes are not within reason and if they come into force they will begin strike action from Thursday January 17th.
Talks between the sides at the Labour Relations Commission (LRC) have previously failed to break the deadlock.