The National Bus and Rail Union (NBRU) is appealing to management at Bus Eireann to enter talks to avoid an all out strike on Sunday.
The industrial action is expected to cause significant disruption as the dispute over pay cuts escalates.
Strike action - including a picket Sunday - comes after 83 percent of union members are refusing to accept cuts worth 5 million euro over the next year.
Bus Éireann has racked up losses of 27 million euro over the past 5 years. The government says its very future depends on this cost cutting plan.
The semi-State body has warned that employment cannot be guaranteed in the event of a strike.
General-Secretary of the NBRU Michael Faherty says the time for talking is now before the strike starts.
And he says there is no way to tell how long the action will last.
"We're worried for the people who travel with Bus Eireann - and we would at this stage appeal to Bus Eireann management to take in consideration their customers; because without the customers, there's no need for them and there won't be a need for us" he said.
"I would at this stage appeal to management, because the management selected tomorrow as the date - it means that we didn't - we're only reacting to something that happened" he added.